The greatness of this game relies on three key elements: atmosphere, story and replayability.
As you might have read in the other reviews, the atmosphere is very good. Play this game with the lights turned out and the volume turned up and you won't know what hit you. There are very little games that are as spooky and freightening as this one. You can really feel the emptyness of the space ship (where the game takes place).
The story is brought through transmissions you receive. Although this might not sound as a good way to present a involving story, it is in this case. It all adds to the overall feeling of loneliness on the ship.
Because there are some many career paths and possible "upgrades" there are thousands of ways you can finish the game, this is really a game that screams to be replayed a few times.
It might be a little slow at times (p2 300 with tnt2), although the graphics aren't that complicated.
The entire endgame is extremely hard and you should be very well prepared before you enter. There is however very little warning when this finale starts and almost no indication about the amounts of equipment you will need (a lot and very heavy stuff), so you might have to replay the game if you haven't watched out (or you could resort to cheat codes).
The Bottom Line
One of the best games ever, very good combination of RPG, action and adventure.