Feedback:
1) Control scheme was not as intuitive as it could be. Maybe it would be more obvious on an iPhone using my finger? I lost 95% of my health trying to figure out how to move my character.
Not a big deal since I could restart, but I was frustrated and might have left if I wasn't trying to figure it out : )
Also problematic is that this leads me to keep accidentally using up grenades because I keep thinking the intuitive behavior is to click-to-move, not drag-to-move.
2) Something of help could be to show gun ranges, so you know better how to move / draw a path.
3) Bigger issue: it would be very helpful to have a notice or info on what the kinds of Zombies are and what their special abilities are. Tutorials can suck, but even a few lines of text might help here, or something to help out the novice player. Likewise how to use health packs.