Maybe a Block Life mod, including the hl2 weapons [Including a few special bricks compatable for a gravity gun, so we can pick up the bricks and throw them around?] And make it a bit compatted with the hl2 zombie mod (Its in development.) and special item adds (Like it can add Rebel Bots and Combine bots, Citizen and Alien bots)? If you start on it, I will allow you to post some screenies of development for bots and other items.
Second thing at mind: RELEASE A LEFT 4 DEAD WEAPONS MOD with WORKING handhold please. getting annoyed of weapons like a minigun being held with 1 hand.