The problem with this movie--it was trying to do the movie, "Blindness"
I have a sneaking suspicion that Cuaron was influenced by the movie, Blindness, because this and the film are structured the exact same way:
1. Plunge the audience into a hellish experience of being deprived of something (blindness, weightlessness)
2. Do a reversal in the very last scene where the experience is lifted, forcing the audience to get a renewed appreciation for sight/gravity.
It worked in Blindness because it successfully immersed you in this bizarre scenario where everyone in the world had seemed to go blind. It didn't work in Gravity because the movie didn't feel immersive at all; it just felt like a generic action movie in space.
Plus, Gravity became one repetitive drumbeat of: this bad thing happens, then another bad thing happens, then another and another and another. I became disengaged halfway through the movie precisely because every time Sandra Bullock got herself out of one situation, I knew it would be the set up for another bad situation. By the time she got to the capsule, I checked out.