Remember in 2001: A Space Odyssey when there is a 15 minute space walk to go out and retrieve a faulty circuit? We had to watch that entire process unravel and listen to the actor breathe, because there's no sound in space, so all you heard was his breathing inside his helmet, right? Remember how deliberate that scene was?
Well, with Inception, remember how Arthur was floating in zero gravity and wrapping up the bodies and taking them down the hallway to the elevator, and setting the charges? While, at the same time a van was falling off a bridge in slow motion, and Eames was fighting projections in the snow, etc.
There is just so much attention to process, detail, and rather than the movie being "hard to understand", it just has lots and lots of detail, process, and deliberate unravelling of the processes, and this is kind of what the story is about - it's almost all about its process of unravelling itself, with the emotional element thrown in with the loss of loved one, and father-son relationship. Since there are so many layers of detail and intricate unravelling of this detail, many are confusing this with being "complex", when it's really just sheer, beautiful, high quality intricate detail - it's really a masterpiece - I've seen no other movie like it...
