It was awesome. So conceptually awesome. I think I might have to see it again to really work it out in my mind because it was so twisty. Don't see it when you're tired because you'll need your mind to keep up and you can't risk falling asleep (Dave? ahem.)
Wonderful, wonderful cast, amazing affects, and it leaves you wanting more. One of the best I've seen in a long time.
Go see this movie, you won't regret it.