Nice try
I admit it's a pretty ambitious thing to attempt in your first game, and you've got the online side of things working (by the looks of it). But, asside from the problems mentioned by other people, it wasn't that interesting. I thought there was a lack of objective, i.e. stand there and shoot as many zombies as possible. Have some sort of storyline, with several levels, where you and your mates can progress further and further. More weapons, more levels, character customization? better animation, better sound. I know this sounds a lot, but it's what I think this game needs to become the frontpage title it deserves.