If you are an AvP Fan, then this is an instant buy. But if you are not you might enjoy this game.
Single Player- It's what you would expect, 3 campaigns featuring Aliens campaign, Predator campaign, and a Colonial Marines campaign.
Aliens'- they move very swiftly, they can climb on the wall, and has 2 attacks. Primary attack is it's razor sharp tail, and it's secondary attack is clawing.
Predator-Moves alot like Marines, but the predator can use heat vision to see enemies, they can use a cloaking device, and can use it's spears and claw.
Colonial Marines- If you play alot of CoD games, then this is probably the class you would be best at. It's what you would expect for a Marine's attacks would be, a gun, and melee. The most distinct thing about the marines is that they are the only class to have a radar, and to have long range weapons.
The good- campaign lasts awhile, all classes are unique, multiplayer is fun, great atmosphere, close up kills are gruesome.
The bad- controls are awkward compared to other FPS, multiplayer could be fleshed out a little bit, level design could be more fleshed out too.