Aliens vs. Predator improves on the first one greatly. It has great action, weapons and a great interlocking story.
The weapons for the Marines and Predators are great, plus the Alien is awesome with its tongue bite, tail whip, claws and pounce. And the story was written very well, it all locks into place nicely and you are not kept out of the loop (although your character might be). There are smart remarks by Marines, great daytime and night-time fights, as well as an awesome ending to further add to the conspiracy.
There are 7 hard pumping missions for all three species and you are not let down. The cut-scenes are great and there are areas to explore (not that you need to) which may give you more health, armour or ammo. The big bonus with this game is the fact that it has a great multi-player. Although there is no fighting computer players, it is great fun sneaking up behind a friend and giving a loud taunt and then ending their existance.
The Marine missions are based around Harrison, the Alien is based around a standard alien drone (from humans with no mutations or abnormal characteristics) and the Predator you fight as is either a Prince or very rich. This game has got great action and adrenaline pumping missions. It is most certainly a credit to the Aliens and Predator Series (do not forget it also makes the Marines awesome as well).