Our studio has a game (we've posted on TA so I won't threadjack by naming it) that has Zombie in the name. Not the same genre at all, but like some others said, in hindsight, I would avoid the word zombie, just because the searches for that word are too overcrowded by all types of zombie games. It took us doing some creative key-wording so people would actually find it! The rigor mortis one is cool! Is there anything out there with that name? I'd search around to test it.
I've added new screenshots in the first post and here is a new web build http://butterflyware.com/webbuilds/zombieGameDark/zombieGameDark.html
Zombie games are best with night AND day. Zombies would become strong during the night, giving you time during the day to chill and grind some points
Rigor Mortis gets my vote. Very cool name, and lets me know it's about zombies without immediately being marked as "another dumb zombie game."