Evil Avatar has the full review:
You'll gain a multiplier by killing enemies in rapid succession, the multiplier maxes out at 10 and only lasts as long as you keep up the mayhem. This brings some strategy to the game. If you want to max out your score you'll want to let the screen fill up with as many enemies as possible, which of course makes it harder to survive. There's also a bomb attack which you gain by collecting little pink triangles. These triangles are conveniently expelled from enemies like pinatas at a 5 year old's birthday party. YAY CANDY!
There's a local co-op mode, but the lack of online co-op is SEVERELY disappointing.
Be sure to read the full review.