So the Project Zomboid team has been really good about keeping people updated since getting green-lit on Steam. Their most recent blog post, features a really awesome display of the game's "sandbox" options.

I personally like my zombies slow and dumb, but if you want I-am-Legend-esque near-human zombies , or simply want your Zombies to run a la 28 Days Later, you can have them, I think this is an awesome feature and i can't wait to mess with it myself. You can buy Zomboid on their site now and get an older test version of the game with the Steam version coming in the near future.