It was fun! I managed to score a pile of pre-screening tickets for the computer club on campus. We had about 30-40 students at the show.
The good: I enjoyed the effects, Matt Damon was very good. 3D was well done and didn't seem gratuitous. It really felt like I was on Mars. Seemed like some decent science and reasonably believable. Good story and good climax, fairly nail-biting. Some truly beautiful panoramas - they managed to strike a nice balance between Mars being bleak, deadly, and unforgiving, but also spectacularly beautiful at the same time. Best character - Benedict Wong is the lead rocket scientist; it's a bit part (and not even credited in IMDB!) but he steals every scene he's in.
The bad: A bit formulaic/predictable. A few really terrible casting decisions. Every woman in the movie looked like a supermodel, whereas the men were more diverse/normal-looking. Script was at times a bit juvenile - the humor was fine, it's just that overall language was more like high school, rather than NASA - more thought could have been put into crafting the dialogue. I don't remember there being a memorable musical theme - most of the music was older pop hits. Some missed opportunities for character development. Rushed, didn't get the sense - at all - that several months had passed.
Overall, I enjoyed it and would happily see it again.