Spoiler Level: Kinda' on the high side, but in a more general sense.
Very cool. I've always been fascinated by dreams, and this film really takes the concept of lucid dreaming or dream walking to new heights. (Or is it depths?)
I rather liked the idea of having a totem to let you know if you're in a dream or not. I've got a similar thing, only in reverse-- I can fly in my dreams, so there have been times when I wonder, "Am I dreaming?" and if I can lift off the ground and hover there, then I know I'm dreaming, and if I can't then I know I'm not. And yes, I have tried when I'm awake. 'Cause sometimes life is just so weird (or so good) that you're really just not positive.
When you go into a movie about dreams, you're already expecting the most obvious twist-- that the entire thing was a dream. This movie plays into those expectations quite well by not going for the obvious, but instead simply planting doubt.
I loved the layers upon layers upon layers. I was hazy on a few details, but when my wife walked in for the last half hour and I had to explain everything that was going on up to that point I seemed to have it all down, so I guess I understood it all okay. Still, it's a movie that I'd probably get more out of seeing a second time.