I was playing this game with Nemega from the start and I loved it from the very first moment. I think this is a revolution in fangames. A co-op game in a browser, I never saw something like this before.
The game itself got great gameplay and nice visuals. There are so many different kind of gimmicks and they aren't overused.
It isn't that long, there are in the moment two stages and 4 bosses( two normal and two secret). But there will be added a third stage in the future.
There is also a single player. But multiplayer is much more fun.
The only thing you need to look for is that you play the game in a Chrome-Browser, else it could get really laggy.
I highly recommend this game. You will miss something if you don't play it