As hard as it may be to survive in a vacuum, it is equally hard sometimes to review a movie in a vacuum. Actually, no, that's not quite right. Wrong step in space, and you die. Wrong step in a review, you just become so tedious that people on the Internet tell you you should die. But I'm sorry - much as I'd like to stick to discussing my opinion and mine alone, I cannot completely keep my mouth shut as wave after wave of old-guard critics who have ranted about the awfulness of CG and Imax and 3D and big-effects movies day in and day out simply roll over when the name Alfonso Cuaron becomes attached. Oh, what's that? It's story that matters? The story of Gravity is self-critiqued in its own third act, when Sandra Bullock says there are only two ways it can end - she dies, or she doesn't die. The same is true of every beat of the movie up until then, except that there's really only one way it can end most of the time - at the very least, she won't be dying off before the big climax.
What I suspect older critics are falling for is the lack of aliens and super powers. It isn't effects they hate at all, so long as those effects are in the service of an ostensibly realistic story, like Titanic. It's fantasy. And while there are one or two things that stretch credulity just a touch, the space technology stuff here seems feasibly real, and the sound design is aces - unlike in the noisy trailer, this space is silent save for whatever you'd hear inside the suits...and a haunting, minimalist score by Steven Price (Attack the Block). Make one of the astronauts, let's say, Hal Jordan, give him a ring almost out of power, tell the same story, and I'd bet at least half the people adoring the movie now would be hating on it.
Considering the source of the jeopardy in this film, it could practically be a comic-book adaptation. Because they're apparently insane or stupid in the near future, the Russians decide to take out some of their old satellites by firing missiles into space at them, creating a huge cloud of high-speed debris that promptly disables half the actual working satellites in orbit. It also causes big problems for NASA astronaut Matt Kowalski (George Clooney) and specialist Ryan Stone (Sandra Bullock), who is not a fully experienced astronaut, but crucial to installing the all-important MacGuffin circuit board into a space telescope, where it will fulfill its purpose of kickstarting the movie's plot. Showered in satellite bits, the shuttle is destroyed, and all astronauts not played by famous people killed. With a limited air and battery supply, Stone and Kowalski must spacewalk to one of two orbiting stations - one Russian, one Chinese - and hope that the emergency landing pod will still be intact. (I'll be honest - I don't know how real the whole "emergency landing pod" thing is. I suspect it's a stretch, but it's convincing enough for the movies.)
So yeah, this is different from Open Water, in which the protagonists were helpless and entirely dependent upon a deus ex machina. Nobody is coming to save Stone and Kowalski, so they have to move quickly if they're going to live. And when they become separated, we're basically looking at one person, namely Bullock, (give or take other voices over the com) for the rest of the running time. It's a testament to Bullock that she can handle being the sole focus, but aside from the metaphor that she was an emotionally isolated person back on Earth (dead kid), and now she's really literally isolated, there's not a lot of deeper drama going on. It is, predominantly, Sandra Bullock versus special effects.