The game's content (ex. perks) was really just gameplay fodder...
The controls were confusingly unbalanced, it was hard to understand what was going on. I didn't play the game long enough to see if anything would change over time, a lot of the apparently 'game changing' factors didn't seem to effect the basics at all.
Your characters moved at a decently fast speed that couldn't be slowed, so it really sucked that you had to be a metre away to attack zombies, while your characters moved a metre per second, which lead to an easy death.
How could a potentially okay idea go so wrong?