Not a very deep game, but fast and fun with all the slimy alien shooting you can stomach and then some.
Aside from the campaign, there's two "survival" modes. These are greatly stripped down action modes. The "career" survival mode has a very simple RPG mechanic that also lets you choose a weapon when you level up. The "stand firm" mode does away with RPG mechanics entirely and just throws increasingly tougher monsters at you along with the occasional boss that drops a considerable weapon upgrade. Unlike the campaign, neither survival modes can be won, it's just a matter of getting the highest score.
There's five types of weapons: Pistols, Shotguns, Machine Guns, Rocket/Grenade Launchers, and Power Arms (Flame Throwers/Lasers). Each type performs somewhat differently, with some types having more than one kind of weapon, so this introduces a bit of variety into play. There's also a few useful gadgets like implants (which grant skill boosts), radar, sources of illumination, and floating defensive bots.
Alien Shooter: Vengeance is nothing to write home about, but it does have quite a bit of visceral action as you gun down seemingly endless amounts of slavering aliens. It's a $20 game but, rather than being an excellent deall, it's more like that's about what the game is worth.
This game has multiplayer support over a LAN. I've yet to try it, but it might be fun. I've heard that it does not play coop over the campaign and, if so, its application may be limited.