Not a bad game, honestly.
I enjoy having the ability to upgrade and customize quite a bit, so it was a joy for me when I saw the different skills and the levels they could be upgraded to.
First, Shotguns seem to work better at range than the Assault Rifles and vice-versa. The spread on the shotguns and unlimited range allows you to take out multiple zombies at once, but up close, all the buck is wasted on a single zombie. The opposite felt true of the rifles, which felt clunky and random at a distance but very useful at short range... I often times found myself firing at the same zombie for a few seconds before finally hitting him, then mowing down the enemies right next to me.
Second, why no center fire?
Now for some suggestions: New "maps". I'll admit, it's a really minor thing but small cosmetic changes to the scenery really make a repetitive game like this seem less boring. Not that I didn't enjoy the game, I just got tired of seeing the same crossroad over and over.