The first thing to say about Gravity is that it's a beautiful movie.
It's beautiful in the same way that Life of Pi is, just spectacular to look at. What's even more impressive about that is that it's nearly all digital. It's pretty amazing. In fact, the movie, much in the way of the Star Wars prequels, was delayed due to waiting for the technology to get to a place where the environment could be made to look realistic. Well, I've never been to space, but it looked amazing. I'm not actually sure it's Oscar material, but I won't be surprised if it gets a nomination for best visual effects.
The next thing that has to be said is Sandra Bullock was amazing. Even more so when you consider that she's the only character through much of the movie. The only other thing like this that I've really seen was the under-appreciated Moon with Sam Rockwell (seriously, you should see this movie). Most of acting is, in a sense, reacting, the interplay of characters (and actors) with each other. It's much more difficult when it's just... you. Nothing and no one to play off of. The dependency on monologues in Hamlet is one of the reasons it has long been considered to be the measure of success for actors. If you can pull off Hamlet (the character) believably, you can pretty much do anything. I think Bullock could pull off Hamlet. She carried the movie as if it was weightless. And, if it doesn't get nominated for anything else, Bullock certainly deserves a best actress nomination for this.
However, I do have to say how very disappointed I am with Cuaron that Bullock was, basically, a default choice, because they couldn't get anyone else to take the park. The anyone elses, other than Angelina Jolie, all being "young, hot" actresses that, well, can't much act. Most of them. Basically, they wanted a pretty face for the role (a role which would require the actor to carry the movie), not someone who has proven she can do the job. That is... just disappointing. But I digress...
The only negative I've seen about the movie has to do with Clooney and how Kowalski is such a flat character. As such, Clooney didn't do much acting. And that's true. Clooney was pretty affect-less, but I think that was intentional. He's not a real character; he's a representation of the person Dr. Stone sees him as. He's the strong leader that takes charge and isn't flustered by anything; at least, that's what he is to her, so that's, also, how we see him. So, yeah, the part didn't require much of Clooney, but I think it was perfect for the movie. He's so flat that we don't get attached to him, and that's required, because we, as the audience, are supposed to be focused completely on Dr. Stone.
Here there be dragons... um, I mean spoilers... Here there be spoilers. You have been warned!
As great as the movie is on the surface (and it is great just taken as what it is, a disaster movie in space), I think it's its deeper, metaphorical meaning that gives the movie greatness. After the disaster occurs, Kowalski needs to get Stone talking so as to distract her and calm her down, so he started asking her questions about home. We find out that, really, Stone has been leaving in space for a long time, since the death of her daughter through an unfortunate playground accident. The woman has no life. She goes to work, presumably doing something that relates to saving the lives of kids who have had similar accidents, although we never find that out, and, then, drives. Just drives. In silence. She has put herself as close as she can into a vacuum. Into a suicide-less death.
The death of Kowalski puts the loss of her daughter into perspective. Stone is trying desperately to hold onto him, but he can see that her persistence is going to kill them both, so he entreats her to let go, just let go. And it's here that we can see the flatness of Kowalski best. He's stoically heroic. There is no clinging to life on his part, just pragmatism. "You have to let me go or we'll both die." He is the sacrificing hero as seen through her eyes. "You have to let go."
Of course, this has a deeper meaning that applies more to the fact that she is still clinging to her daughter than it does to him.
After that, she enters the space station and strips out of her space suit, and there is a lingering image of her curled, fetus-like, in front of a round window looking out at space. It is the exact image of the womb and of her entering into a state of rebirth.
But it's not really that easy, because birth, as easy as it seems (to us in the USA, anyway) in this 21st century world, is not easy. And she almost gives up a little while later but has a lack-of-oxygen induced hallucination of Kowalski telling her that she has to make a decision: She has to decide to live. If she's not going to decide to live, she needs to quit living the lifeless life she's living and just get it over with. She switches the oxygen back on and chooses to live. Finally, she lets go of her daughter and says goodbye.
The final scene of her crashing down and escaping the capsule as it floods and sinks, the scene of her climbing out of the water is the very metaphor of birth. She stands there on shaky legs (after being in a zero G environment) like a newborn colt and faces a new day. A day with the hope of life, not one that clings to death.