Not bad. Not really anything very new, but still quite enjoyable anyway.
Generally, the graphics were pretty good for the time when released, and the atmosphere is very good. The story is weak, and several of the areas designs were being used over and over in the course of the game. Most of all of that is a big blur now, but I do remember enjoying both the difficulty and some of the more clever scenarios.
Sure, there are a lot of shooters out there, but I found this one to be a little more compelling than Quake 2 for instance. the weapons are good, and some of them are REALLY good. I hesitate to recommend this to everyone - it can be a difficult game, and the atmosphere is very dark. But if you like that kind of stff, it's enjoyable.