Inception is a psychological action/drama/thriller with layers of complexity. The fundamental premise is interesting in and of itself: the nature of dreams - to what degree are they controllable? In the end, though, it's the way the movie expands on and brings this and other themes to life that's amazing and impossible to explain.
Great visuals and acting make Inception mostly believable, in a great-action-flick sort of way.
In a nutshell, it's a 2.5 hour action film that never feels dragged out. It's tense and harrowing, but not scary or sickening. It forces you to think, but not frustratingly so. It offers remarkable depth whilst avoiding paralyzing convolution.
All in all, this is a great show that I plan on seeing - and getting a lot out of - a second time.
**I don't regret indulging in "The IMAX Experience" for my first viewing, but haven't seen it at a standard theater yet to compare. As you might expect, the audio/visual was awesome at the IMAX theater.**