I have to say that this is a fantastic game, Despite what other reviews or people have said, the graphics are very good with some excellent detail, the lighting is spot on and the audio is awesome.
The 3 campaigns are very diverse and unique but are challenging on the higher difficulty levels which make them fairly lengthy, and is the same length as a normal FPS. The multiplayer is again unique, with various modes like Predator Hunt and Infestation, as well as the normal Deathmatch and Team Deathmatch modes.
However, the best mode is Survivor mode, which can be played in solo or upto 4 player co-op, where you have to fight off wave after wave of Aliens, which get progressively harder and basically you have to survive for as long as possible. This mode is not a rip-off of the Horde mode on Gears of War 2 as the original 1999 AVP on PC invented this mode, and it is downright frightening.
Also, those people moaning that there is no Aiming Down Sight and Crouch controls, the reason for this is that you don't need them. If you watch all the films, you don't see people crouching or aiming down the sights of their guns when they are being hunted or confronted by 9 foot killing monsters. This not a war game it is about survival!
Also, in relation to the criticism of the lack of maps, the game's developers, Rebellion, have said that lot of DLC will be forthcoming, and the Survivor Edition, which I have got, comes with 4 extra maps, 2 for survivor mode and 2 for multiplayer, and these will be available in a months time for those who bought the normal version.
Overall, I rate this game as highly as COD: MW2 and Gears of War 2, as it is unique and different in its own way. It is gory, violent, terrifying and just as immersive as the films, and has sold really well so far I have been told, which hopefully means a sequel will be on the cards. A must buy!!!!!