[quote name='Stele']Why does this game have such bad reviews?[/QUOTE]
The game has a low-budget, B-movie feel to it, but it was never intended to be a full featured $60 game anyway. The series actually has a bit of a cult following. At times the previous game can fetch up to $20-30 used on eBay.
The best comparison I can think of is a online co-op Smash TV. Or maybe you could describe it as Dynasty Warriors with guns and enemies that are as tall as buildings. The lower difficulty settings are actually a bit boring, but once you step things up the action reaches levels of absolute insanity. There's a level-up mechanic and simple loot system in the game that are constantly rewarding you with new weapons to mow the endless waves of enemies down. It's by no means a deep game, but it is still a hell of a lot of fun. I bought when it first hit $20 and have had no regrets in doing so.