Awesomely oppressive! To those it might interest, there are simple hacks to easily bypass limited in-game saves via a command line parameter or assigning keys to quicksave and -load.
This game is interesting because it is not a mere shooter set in the Alien or Predator universe. It offers a gameplay experience that differs from other shooters. Even the most classical campaign as a marine is original. You have to be a sharp shooter, fast and precise, because aliens move incredibly swiftly. The very second you see them, they are on you. Weapons are powerful and localized damages encourage headshots providing that you have enough time to aim. You can literally tear aliens into pieces. The player is always on tenterhooks, progressing carefully, watching for an alien ambush. Each encounter is scary. The tension is kept at a climax thanks to an overdramatic music, dark levels and unpredictable enemies.
As for the other playable races, both are fun, it is very exciting to play non-human races and kill humans, it is as reversing the roles of hunter and prey. About the Alien, there are no such things as floor or roof, you have to think in 3D. I found it rather hard and bewildering. This leads me to the major downsides, the level design that can be a little mazy, with complex textures. I often found myself stuck, not knowing what to do or where to go, reading the messages again and again. The problem is that enemies keep spawning randomly. In many shooters, you often come to the point when you have cleaned the level and there is no threat left. In AvP, you never feel safe. If the game lasts too long, it becomes increasingly oppressive because you might run out of ammo. Highly worth the try!
