Disclaimer: I am not a film studies major. This is a snapshot in time of my evolving taste in film, not a permanent benchmark. My opinion may change at any point, and when I do I may write another post like this.
Film is a form of art with visual, audial, linguistic, literary and cultural dimensions. It is not something that can be objectively measured for quality; the closest thing we mere humans can do is arrive at some context-based limits, structures and expectations when appreciating other people's art work.
Collectively we might arrive at some consensus as to which elements we react positively, and that we declare as 'good'; I feel that this is much more so in the case of movies. Films that tend to ignore these limits and expectations are in fact closer to self-expression than most Hollywood productions, hence they get the label of "art house" (this is not to be confused with "independent" films which may still follow the Hollywood standards and genres in film-making, but simply not financed by big studios).
Unfortunately, I don't have the time or experience to explore the much wider and fascinating world cinema, and most people are more interested in what's "now showing" in the theaters anyway, so I will only talk in terms of Hollywood-esque films and their appeal, design, influence and content to the mainstream audience.
Animated films have become increasingly abundant, popular and successful at the box office in the past two decades. While when talking about successful animation studios, Pixar always tops the list nowadays, both Disney and Dreamworks have caught up considerably with some recent films. Some examples I can think of in this category includes Kung Fu Panda 2, Megamind, How To Train Your Dragon, and most recently Wreck It Ralph.
However their success is not in appealing to the children, but being able to attract people from all other age groups as well. Why are teenagers, young adults, parents and even elderly people watching these light-hearted, innocent films that were intended for your kids or younger brother/sister? A closer examination shows that while these films are simple enough kids can follow, they are often littered with adult-directed humor, cultural references, deeper themes and at times even evoke the childhood in us and engage it with wonderful nostalgia.
Films that I consider good should be a good movie to watch even if it's not your 'thing'. They should cater to their intended audience, be it teenage girls or war novel lovers, fantasy geeks or trekkies, but not be so exclusive in its production and delivery. Insider jokes are fine but if they are a prerequisite to enjoying the film then it is what I consider a film for fans; a movie that is only marketed and sold to its most loyal followers.
Having said that, I do have films which I love despite being a film very few would appreciate as extensively, and this I refer to Joss Whedon's "Serenity", which was a barely-broke-even film made for the diehard fans of his short-lived space western TV show Firefly. When my dad saw this film he thought it was a decent movie but didn't like it, as there is so many characters and history to the world that he doesn't appreciate as he never saw the show. So to me, the intended audience, Serenity was a great film, but to my dad it was just an okay film.
A film that appeals to their targeted audience is important, but I believe it is really good if it can appeal enough to a wider sphere of people, even to some limited capacity.
A memorable film tends to have a strong vision and distinctive design.
When I say design, I refer to all aspects of the film: the design of the characters, the design of the sets, the design of the costumes, the musical design and even the design of the dialogue.
I'll use Star Wars as an example. Despite how forgettable the plot to the prequels are, every time I hear those iconic orchestrated musical numbers, it evokes wonderful memories of the original trilogy; the scale and sinisterity of the world we are being immersed into, and the drama which often is more pronounced in the music than on the screen.
In fact, one of the better things to me about the prequels are the backdrops. Yes most of it is CGI, and the actors were basically in a green room most of the time, but the worlds generated around the characters were very distinctive. They were thematic, and most of the time well-suited to the atmosphere. I can tell where I am in their universe through each scene in the film without text overlay to remind me. Having said that I couldn't care less what's going on with the characters as I'm just waiting for the highly choreographed fights scenes most of the time.
Visual design is very important because it is the first thing we the audience see. Once those colors, shapes and layers enter our eyes it establishes our expectation for the rest of the film. We are programmed to connect certain types of atmospheres with emotions, like darker settings is to evil, or orange/red color filters is to passionate love, or washed out grey, green and blue is to medieval cities or some dirty ghetto.
The original Willy Wonka film did this particularly well by contrasting the plain ordinary world with the whimsical colorful candyland that was inside his factory. You really do feel like the characters have crossed into another dimension and are pleasantly surprised by how contrasting the real world is with Wonka's world, though the reason he had that scary tunnel was kind of awkward.
Character design would be the next most important design aspect for me. I find that most people like the characters that are either a pillar or a revelation within the story. I better explain. A pillar character is one whose personality and triats we are fully aware of, we know and understand their motivation and desires, and for most of the film they don't change because that is "who they are". You see this a lot in TV shows too, like Sheldon in The Big Bang Theory, or Homer Simpson in The Simpsons, or Masuka in Dexter. They are our refuge for something familiar and predictable, often in a story that is evolving at a fast pace and constantly challenging or changing our perception. They're not always comic reliefs like the ones in the short list of examples, but they tend to make us feel safe, like even when the world ends at least we can count on them to be them.
On the other hand, a revelation character is one who we don't know much about at the beginning, but over the course of the movie we gradually find out more and more about them, sometimes in step with them discovering more about themselves as well, and during the climax of the film we find out the most important facts, which greatly impacts the resolution of the film. We see this a lot in character-driven stories like Cobb in Inception, Wolverine in the X-Men series, Bruce Banner in The Incredible Hulk, and Po in Kung Fu Panda 2.
A revelation character has the exact opposite impact on the audience as a pillar character. They challenge our preconceptions about the admirability or despicability of their actions and attitudes, they make us curious about how their journey will pan out. They are often at the center of the drama or conflict, and often are the cause of it too, and they keep us invested in a film that may be otherwise formulaic or uninteresting.
The absence of the pillar and/or revelation characters does not immediately ruin the film, but certainly increases the difficulty of maintaining audience engagement. Some good films give you everything about each character, which tend to be somewhere along the spectrum of the pillar and the revelation, and is more of a "lets mix them in a beaker and see what happens" type of experience. Buddy cop movies, crossover films (like The Avengers) are like this. You already know what each character is like, you already are to some degree invested into each character, and the ensuing chaos they must face together builds and breaks them, thus developing them further, refining or enlarging their traits, and not always for the better, which is what draws us further into their conflict.
In a way the pillar and revelation character are the extreme ends of the character design spectrum, and I would argue that a good film needs characters that fall on different parts of the spectrum. If they're all pillar characters the story or challenge they must overcome needs to be really interesting or the ending/resolution will be too predictable (e.g. Power Rangers, Twilight, Transformers, Care Bears), but if they're all revelation characters it leaves the audience no time to breathe or relax because there's too much at stake and the outcome of the film may be too unpredictable for the comfort of the viewer.
A film which challenges or changes a viewer's preconception about the world, educates them about moral grayness, or simply opens their eyes to the perspective of a minority group they've overlooked in the past, is doing something good. However it doesn't always have to be positive, and it doesn't even have to be useful, it just has to influence us somehow.
Many future-oriented films speculate about what might become of Earth in the near or distant future, either through a post-apocalyptic or post-enlightenment scenario, and more often than not human nature or human action is what caused the downfall of civilization in the past, or its downfall in the future. These films, while being fantastical in nature, generally serve as a warning of the path we are travelling on right now and its dire consequences. Sadly few of them succeed.
Animated films are again a stronghold when talking about timeless tales and movies with influence, such as Disney features in the 90's and Pixar/Dreamworks in the present (e.g. Wall-E with environmentalism, Up with attachment, Kung Fu Panda 1 & 2 with choosing your own destiny). Films that are not only entertaining but teach our kids important lessons definitely are worth the trip to the cinema.
On the other hand influence can be oriented around an individual rather than a genre. Some great directors such as Quentin Tarentino, Christopher Nolan and Mark Scorcese are also influential because they have each mastered and refined certain elements of the film medium, and thus any of their production would carry their signature. When we see any film by them we can immediately identify their fingerprints. For instance, Tarentino's Django Unchained has been dubbed by many critics as the slavery edition of Inglorious Bastard due to the same level of brutality, how bare and honest a portrayal of the era and environment his characters are immersed in, and the abundance of beautified violence and gore throughout the film.
This is of course also true with actors/actresses. When I see Johnny Depp, Cate Blanchette, even Kirsten Stewert (*sigh* I know), no matter what role they're playing I always remember them by their most iconic character. Okay before I get eggs hurled at me for implying something positive about Twilight I better clarify; not all good films need to influence us in a positive way, but not ALL films with influence are good. I mean thanks to Twilight studios are now beginning to take adapting young adult fiction as serious franchise opportunities. Some other 'bad' movies like Batman and Robin and Battlefield Earth are equally impressed into our memories; no matter how hard we try to forget them they will forever haunt our subconscious. They fall into the "so bad it's good" category.
Regardless of where the impact or influence comes from, a film that can leave us with deep impression of the characters, the style, the music, the story or the message, is doing something right even amidst a mountain of not making sense, offensive or completely out of touch with reality. Many of the 'greatest films of all time' as well as 'worst films of all time' have significantly influenced their generation, working their way into our culture, our humor, our very identity, and some even continue to influence the curious youth who may accidentally stumble on an older classic by chance.
They form the bible of cinema, because they can survive the test of time and competition, and no matter how many other films we bombard ourselves with, we just need to hear that iconic song (e.g. My heart will go on -> Titanic), or hear someone utter that line (e.g. "I"ll be back" -> Arnold Schwartzenegger), or see that face (Leonardo Decaprio character -> Leonardo Decaprio) and our minds can only wonder back to the world of that film. A film that is impressed in us even 10 years after seeing it definitely has something good about it.
When I refer to content I am talking about the actual meat of the movie. The plot, the dialogue, the action, the things you see happening.
I left this last because often I find most moviegoers don't really remember most of the film after a week of seeing it. They can remember the music, the actors, some catchy lines or iconic scenes, or maybe the overall feeling of the film, but when it comes to the plot and complications, few actually can hold a conversation about it without a quick rewatch.
However, as a person plagued with eidetic memory when it comes to movies, I can play the whole film in my head. And when I experience a film I experience more than those peaks and troughs, or the general emotions. I also experience everything in between; the expository dialogue, the less important character interactions, the filler scenes. So a story that doesn't make sense or doesn't flow well over the course of the film tends to throw me off even if it does have an epic climax or a particularly good scene.
You know a film has problems if it doesn't keep you engaged during the entire film. For example, with Twilight Breaking Dawn Part 2, I was practically asleep the first two hours, until we got to that epic climax which woke me up briefly, but even as I wrote that review all the scenes ridden with pedophilia and weak romance keep disturbing my train of thought. The Hobbit had a similar problem, though it was more a pacing and padding issue than an entire section of the film being bad.
In my opinion, a film should be as long as it needs to be, but no longer. I feel that with the recent resurgence of film franchises, movie producers feel guilty they take so long to produce each film in the franchise, often releasing each film in the franchise with 2-4 years gap in between (contrary to urben legend, it's not just a marketing strategy, expensive films do take a long time to produce while pleasing all the shareholders). So to compensate, they also produce a movie that is longer in running time. (if I have time this weekend I might actually do some proper research and sketch up a graph to show the upward trend in movie run times)
While a movie that runs for longer means we get more 'stuff' to watch and thus appears to be more worth our money, if those extra minutes are not substantial or effective in keeping us invested, then they might as well not be there. You're just wasting both the audience and the cinema's time. Again the most recent culprit of this to me was The Hobbit, which should have been a 2 hour movie. God I hope they don't have an extended edition to this.
I can safely say that if a film can satisfy these four criterion of mine, I would almost always consider it a good movie, but remember that there are always exceptions to every rule. This is why I have on my list of favorite movies things like Commando, 300 and Bee Movie. They're not very good movies, but I love them because they know what they are and don't try to pretend to be anything else, giving the most of what they've got and giving it with all their heart. And in a way is good enough