Having only seen Alfonso Cuaron's Gravity in 3D, I'm not sure I can recommend that version as a must-see--but I think the movie itself is. So you should go see it before I spoil the heck out of it for you.
First, the cinematography and all the special effects are pretty amazing. I had no problem believing that this was taking place in zero gravity; in fact, there was a significant portion of the film where I could only think, "The only way to make this would be to film it in space."
Second, the acting: since this film takes place between two people (at most), where we can almost only see their faces (in their space suits), there's a huge amount of weight placed on their dialogues--and monologues. And it's to the credit of George Clooney and Sandra Bullock that those interactions never feel strained or unbelievable. Bullock in particular has the thankless task of selling us on the character of a depressed woman who still has the will to fight for life.
Third, and most especially, the writing: the story here is pretty simple in plot terms, presenting a golden-age-style problem story: After their spaceship is hit by some dangerous debris, how can an astronaut and a doctor get to the space station that will help them survive? There's some typical "do we have enough fuel, what about our inertia" questions that come up in golden-age stories. I mean, it's pretty easy to imagine Isaac Asimov writing this story, with the astronauts figuring out some clever way to slingshot themselves around or otherwise save themselves... with Science!
But as the story goes on, this simple story of physics adds a character and emotional layer, in a pretty artless manner: just having one character tell the other about her secret and ever-living sadness over the death of her daughter. There's no real mystery or drawn-out period where Clooney gets Bullock to trust her. All we get is him coming to rescue her from the deep darkness of space and towing her towards the Russian space station.
But we buy all this because of the weird and intense situation: given that these people can't act physically in the same space, given that they are in imminent fear for their lives, given that all they can do is talk, given that they are relatively new colleagues, we accept learning this backstory in this way. No flashbacks take us out of the moment. No other actors get in our way of imagining Sandra Bullock's dead child. It's really a brilliant way to film something claustrophobic and make that claustrophobia work for our engagement.
I also think the action set-pieces are brilliant little moments of set-up and pay-off. We know the space debris will come back in approximately 90 minutes; we see the little bubbles of fire on the Russian space station; we see the parachute tangled up with the Russian station; etc. Because we feel connected with Sandra Bullock's character in the most basic ways--her voice, her face, seeing from her POV, her newness to space--we jump even further than we might otherwise.