Holy shit, what a movie! It's been a long time since I've seen such an engaging and complex story, one that challenges you rather than spoonfeeding you the answers. At one point the movie has four simultaneous storylines, one nestled within another like an onion, all skillfully arranged and edited together to be easily followed if one pays attention to the details. The special effects were incredible but not overused, and the use of time-warped musical cues within the "story onion" is genius. It's also a very long movie, clocking in at around 2.5 hours, but it's well worth the time.
If you haven't seen it yet, do it now! Even if you're at work, just drop what you're doing and go grab a ticket. Your boss will understand. Then come back and read these for more insights: