In case it needs saying there will be plenty of spoilers to follow.
Perhaps Inception's greatest achievement is that it layers itself in a number of ways. Not only in the actual plot of movie with the dreams within dreams mechanic, but to the viewer each layer is different kind of movie, all wrapped in a sci-fi-thriller-heist movie which is at its core something of a love/deception/letting go film. So there's a lot going on. To its credit the movie manages to present all these things in a tidy and non-confusing way. At the movie's lengthy climax there are multiple dreams within dreams with each moving at a different speed relative to the others. What takes a few seconds in the first layer takes minutes in the second and hours in the third and has happened in the blink of an eye in the real world. So while a lot of things are happening you never really get lost, and you never really feel like you don't know what's going on.
Another thing the movie does well is explain, something it does with gusto. A large portion of it dedicated to explaining the science and rules of entering people's dreams (and then later explaining how those rules can in many cases be bent or broken entirely). Such pains are taken to explain almost (more on that 'almost' later) everything that it ends up being almost completely unsurprising when something supposedly interesting happens. It's the quintessential movie that shows you an example of one thing in a controlled enviornment and then later when that same thing happens in a real world situation beats you over the head with "hey, remember that?!"
This isn't necessarily a bad thing. Hell, a lot of video games utilize that very principle, and I've dedicated a not insignificant portion of my life to those. Of course what works in one medium can be extremely clumsy in another. Games attempting to mimic movies often fall short, but the reverse is no exception. Had I been watching Jurassic Park or Transformers I wouldn't have given this kind of screenwriting a second thought. However Inception knows that it's pretty smart and so many of these moments can come across as being forced, and at the very least they leave a potentially interesting and even surprising thing become something you expected to happen.
I suppose that predictability in movies is not a huge issue. We watch action movies knowing with a high degree of certainty that the hero will win at the end. We watch monster movies knowing that the monster will probably kill some people but ultimately meet his demise at the end. Hell, I knew almost the entire plot of The Aviator before I saw it and and it's still one of my favorite films.
Subtlety is something of a lost art in film making, or at least in mainstream film making (though I make no claims to watching many non-mainstream ones with any regularity, so maybe I'm totally wrong). For a movie that ends on such an intentionally ambiguous note I have to wonder why the sly and non-addressed slip-ins such as Cobb's (Leonardo DiCaprio) totem not being his own were not echoed elsewhere. Arthur (Joseph Gordon-Levitt) explains and demonstrates creating architectural paradoxes to Ariadne (Ellen Page) and the very same thing appears later, saving Arthur's butt in a bad situation. The movie constantly beats you over the head with the idea that maybe there's no difference which reality you chose to live in; the dream or the real world. The audiences thoughts are echoed almost precisely when we are about to leave the second layer of dreams and walk into a third one for the first time when Ariadne asks "Whose subconscious are we going into now?"
I know Christopher Nolan is capable of being more subtle because I have seen Memento, a movie that starts you at the end and moves you to the beginning. You start the film out confused and become more and more confused and then gradually less and less confused until its tragic and fairly surprising ending. Contrast that with Nolan's most popular film, The Dark Knight, where the Joker explains the dynamic between himself and Batman while he's swinging from a building 20 stories up.
I thought for a while on why these situations in Inception bothered me as much as they did and I finally realized it was because the beginning of the movie left you in the dark as you watched it unfold. Walking into the theater you know it will be a movie about infiltrating dreams, so you can guess that these guys are probably in another guy's dream, but that's really all you get. The idea of layered dreams and architects and stealing memories and manipulating worlds is completely unknown to the audience, and so the opening sequence is watched with a good deal of speculation as you try and figure out what's going on. It's fairly obvious that the first world is a dream, but when you suddenly realize what is going on with the second world (which in my case was a few moments before Saito (Ken Watanabe) realized it) it all comes together. The opening sequence actually does an excellent job of pulling you into the science and mythos of the film, leaving you wanting to learn more.
And then you do! After the opening almost nothing goes unexplained outside of Cobb's back story. Even with that, while you have to wait some time to figure out what exactly is going on with Mal (Marion Cotillard) you still kind of get the idea after a few lines are dropped as to her past. Maybe you don't know precisely until they explain it fully, but the path is there for you to follow and when the movie gets to the end of the path it's really pretty obvious that was where the path was going. The "ohhh" moments are few and far between.
Oh right, that 'almost'. For a movie that takes such great pains to explain everything, it never quite explained the concept of limbo to my liking, though perhaps it was left intentionally vague as to remain more ominous. Things that are fully explained tend to be a little less scary, seeing as the unknown is the scariest thing of all (allegedly) then not coming out and explaining what is going on with limbo makes it seem spookier.
My main gripe with limbo was how it was never quite explained whose limbo we were in. If the third layer of dreams took place in Fischer's subconscious (as the movie made sure to let everyone know) when he was killed he should have gone to his own version of limbo. However the limbo they went to appeared to actually be Cobb and Mal's limbo from before her death. So did Fischer go to his own limbo or was he somehow pulled into Cobb's limbo via Cobb's memory of Mal (thus by Cobb himself)? Saito was clearly in his own limbo, but how did Cobb get there? That at least can be explained away since Cobb and Saito were connected within multiple dreams, but limbo itself seemed to be presented in a somewhat shaky way. And yes, I do realize that I am asking for them to explain something when I have been complaining about them explaining too much the entire time. It's different!
All that said, I still think the movie was well done. It was certainly captivating and very visually interesting. Clocking in at just under two and a half hours (by two minutes) I never checked the time once, so clearly I was interested. Well done movie? Certainly. Great movie? For sure. Most mind-blowing film watching experience ever? Not really. Either way I'll take it, I just wish it hadn't given me hope that it would be something truly special.