I liked it
It's a simple, fun game to pick up and play without a steep learning curve, but the challenge is there for those who want it.
Things I would have liked:
-If you had some cheat codes to unlock all the weapons that'd be cool. I understand I'm supposed to work for it but I'm getting kind of tired now that I've already gone through the game 3 times.
-If I could restart with the difficulty closer to where I left off. The 2 times I restarted, I was back to the beginning with only green zombies, then blue, then snatchers. If I could maybe start back off from snatchers or something that'd be cool. I understand it's probably like this to make getting the achievements easy/possible, but I think it'd make a good option.
-Then of course I'd like more depth =p It might take away from a game that's so simple to pick up, but platforming, story(more I mean), different areas, and the like are things that might go well with a game like this.
-I like how you had a variety of guns that felt different. The mini gun was powerful but slowed walking speed and had limited range, which is similar to the shot gun but it doesn't slow you down as much and a single bullet can harm up to like 5 enemies, which is similar to the sniper gun but if someone gets too close the sniper gun is less effective.
-Skins from hard work put into achievements is the kind of thing I like when it comes to achievements. It's a reward, but it doesn't leave lazier types out of the fun. This appreciative comment is a little dickish >o>
-This game has what you expect from it when you play it. It's not misleading, if that makes sense.