There isn't shit else out yet. WarZ is better than people say, you don't know how you like it until you try it. (Even though they lied to everyone about features in the game.) DayZ I'd pirate and play on cracked servers, Left 4 dead is a zombie game (Zombie doesn't mean they have to be dead.)
You won't be finding any good FPS rpgs for a while. The only other "zombie games" you'll find are, project zomboid which is and indie and is still in beta I think but imo looks like it will turn out good. Dead Frontier which isn't for everyone even though it is an rpg 3rd person shooter a lot of people don't like it. Then you have your shitty zombie browser games.