I think this game looks like it'd be fun, especially since it's designed to be coop firstly.
I know there is more out there, but there were about seven gameplay videos here: http://www.gamespot.com/pc/action/left4dead/index.html?tag=result;title;1
I know there is more out there, but there were about seven gameplay videos here: http://www.gamespot.com/pc/action/left4dead/index.html?tag=result;title;1