Time Attack
Keep an eye out for groups of zombies in the time attack mode where zombies will come at you from all angles. Collect weapons around the Comatose map trying to acheive the best score by killing big lines of zombies at once.
Campaign
Collect car parts that are located around the map while steering clear of the masses of zombies that will try and eat you along the way.
its no bad thing (in my mind) to be compared to Boxhead - and you're right, its definitely more realistic!
A fun game.
http://www.thegameslist.com/game/721/Boxhead__The_Zombie_Wars
Good fun