I saw this in XD 3D this week (the next best thing to IMAX?), but I haven't felt a need to post about it until now, for some reason. It's definitely been in my head.
Thoughts: Visually stunning; I was incredibly impressed walking out, and the whole experience was just really immersive. The writing was well done, and the metaphor wasn't too heavy handed, but it wasn't too subtle as to go unnoticed.
Clooney and Bullock were both great; I suppose a flick like this is any character actor's dream, considering the fact that it's pretty much 100% character development and you only have to share the spotlight with one other person. With that being said, it seems like Clooney kind of took a backseat the whole time. He was something of an archetype to move Bullock from Point A to Point B. He did a fantastic job, but, ultimately, I kind of wish they'd delved a little deeper with him than what we saw.
The film really was a roller coaster ride, though. There were times when it was almost serene, and then, there were others where it was virtually terrifying. All in all, though, it was one of the best films I saw this year.