It didn’t really do anything wrong, but not enough right to necessitate its existence. It seemed as though they took a handful of good ideas (and a few great scenes especially), and stitched them together with the 1982 film.
The CG was overused in some parts, and lacked some of the charm of the practical effects wizardry they used in the other, though there were a few bits of awesome here and there. They also started with way too many people, so the deaths start rather quickly and have little suspense built up for most of them. Mary Elizabeth Winstead really seemed to be channeling Ellen Ripley hardcore throughout, and while there wasn’t any bad acting, she also seemed to be the only character that we were really supposed to give a damn about.