An excellent FPS with a few shortcomings.
The combat is a bit lacking despite the AI, which I think is relatively good compared to most contemporary games. You basically have things leap out at you and you kill them, though they do retreat and even try to heal themselves if you haven't hacked a med station. The difference is that they will try to circle around to kill you, which I haven't seen a lot of, though it's still not difficult to kill them, which makes the combat lacking.
Also, the hacking, while fun in System Shock 1 and 2, is pretty annoying. It's great to have a turret/camera on your side, but the flow thing is just annoying. I hacked everything but it was pretty boring. Somehow, in SS2, it was fun, but in this game I'm telling you - it's boring and annoying - although it's obviously useful and sometimes even necessary to keep the splicers off of you.
Without revealing anything that would ruin your enjoyment, I went the save everyone way, and I was a bit disappointed by the ending. I would suggest killing everyone, even the little sisters. The final "boss" battle was a bit short.
Still, looking back at this review I see that I was a bit harsh. While this game is worth 50 bucks if you have the cash, I'd probably wait until it's a bit cheaper. Definitely good, but not that satisfying in the end. Nice 5 second movie and then kicks you back to the startup screen.