A movie filmed almost entirely in low earth orbit, with 90% of the physics being correct - AND a good story to boot. Writing a good story, and then fitting it into the constraints of the real world - especially a world that movie makers have no instincts about - is a significant challenge, one that Alfonso Cuaron did an outstanding job at.
It's a nice counterpoint to the "roll the dice" physics of Armageddon, also discussed here,