Let me state firstly that I am a `mature gamer'(xCCx JAZZMAN on XBOX live)
AVP? Well it's a surprising package really, and depending on your needs, suits at least some, if not most in some way.
Many of us are spoilt with MW2 and its beauty, and AVP isn't really a `beauty', but graphically it still has its moments.
Lets start with the marine campaign, for the purist you may as well look away and not even bother, you can't crouch, use `iron sights', and jumping might as well not be an option either as there really is little or no use for it, there is nothing other than point and shoot and turning your torch on and off, although the motion sensor is a very satisfying toy, purely because (like the pulse rifle) it sounds and looks like the one in the movie, and is a major addition to the whole `feel' of the game from the marine perspective, the real let down for the marine side is a lack of interaction, in addition the whole idea of stealth and giving your position away by having a torch on doesn't really come into play either, there is very little stealth involved with marines, and once you have played the other campaign's you'll see why the torch being on or off matters not a jot as both the aliens and certainly the predator can see you with their `focused' vision anyway.
The Alien campaign is probably the most enjoyable, you do get the pleasure of stealth killing, and more enjoyable is harvesting humans, you get the option to `grab' and kill with a random finishing move, and of course you get to use the infamous `headbite', which isn't the best looking move in the world, but still pleases.
The alien can walk on any surface, but `autoclimb' is best switched off at all times as when you `run' very fast you can end up on a side wall or ceiling quite easily, also the alien has a `focused' vision, this is where humans have a glowing outline (like the readybrek kids if you're that old!) of two colours, red if they pose a threat and green if they can be `harvested', lets not get carried away with game play here, as in fairness there is so little other than stealth that you can do with the alien, which is a good thing.
Predator campaign? Well it's by far and away the poorest, mainly because unless you up the ante difficulty-wise it really is quite easy until the very end.
You eventually get to use all the predator weapons, the disc thrower being the best(which is probably why you don't get it until half-way through) but you do start with the shoulder mounted plasma cannon, and unlike the marine's, jumping is a prime requisite.
The predator is the consummate stealth warrior, and it's hard to imagine why they made him so tough, apart from the fact he has great weapons and fighting skills, he can also take quite a lot of punishment, see everything by way of two modes of vision and the predator achievements are very easy.
Other than a standard manoeuvre-strike fight at the end (which can be tricky until you use the right weapon)it is just a 'by-the-numbers' campaign.
For fans of the films (both alien and avp series) its pretty good, for the gamer its a bit of a letdown as the actual game play is flawed, but still fun if you're not too serious, the campaigns are enjoyable, the multiplayer is good when it works, but neither at any point excel.