Critical mass of zombie games has long since been reached. We are now at the point where the pit of E.T. Atari games was dug up to create a hole big enough to hold all the excess zombie games being made.
I had not realized how bad the problem was until I went to Origins and walked through the vendor hall. There were at least 100 advertisements for zombie games in the first row I walked down, including zombie tabletop games, zombie dice games, zombie RPGs, zombie survival, surviving as a zombie, zombie superheroes, zombies vs. pretty much everything, everything except a zombie cookbook, which Google tells me also exists.
Someone could surprise me with a zombie game that brings something new to the table, but it would surprise me.