Pretty good
This game has a nice twist on the backstory. Instead of fighting to survive as a good guy and eventually dying, you're playing as the bad guy, so when you lose it's like you won sort of... The music is a bit too sad though, since technically losing is a good thing, should the music really be that sad? Anyway, there were a few things I didn't like about it.
First: The faster cooldown powerup is USELESS. Even if the gun overheats (which it rarely does), you can take that time to reload anyway, so overheating isn't really that bad, since you've got a limited clip anyway.
Second: The aiming is a bit off... Enough said.
Last: The cutscenes interrup gameplay, which I found incredibly annoying. They should only appear once the wave comes to an end or at least slows down. I often had one pop up in the middle of an enemy wave, so it threw me off.
However, the concept was good, it could have been pulled off better though.