Eh...
Not the greatest game I've ever played, I have to tell you. Started too slow, picked up too fast. Worst music for a defence game I've ever heard, but it was a pretty nice song though. Just the context it was used in was truly quite dismal. No real climax, didn't add sort of atmosphere to the game itself.
Personally if I had the last keg of beer in the world I'd sell it to the highest bidder before the blackmarkets started selling their own home brewed stuff. Not a bad idea for a game though. I think it would have been better first person though, because the birds-eye view has the advantage of watching all three doors at once. Of course first person would only work if hundreds of people weren't streaming into the room.
For a challenge, try spinning around non-stop and nailing them like that.