Difficult, and little more than a mission-pack, but nonetheless great.
The reasons are somewhat understandable. There was a bug in the original that prevented the higher difficulties from working, and the developers were e-mailed many times saying that the highest difficulty was too easy. They responded appropriately. The new aliens have a tendency to take several shots before dying (or, in the case of crabmen many, many, more.) and the missions are all longer, requiring more ammo, which every gun requires now.
So, what redeems this title? Atmosphere. Combined with the difficulty, this game is even creepier than the first installment. The music, environments and general atmosphere are all top-notch. It's unfortunate that the developers didn't realize what they were doing with the difficulty, but if you play on Novice, then you should be pretty safe.
All-in-all, decent. If you liked the first and want a variation on it, go ahead and get this.