I like it, but I have some complaints...
1) No Jumping is a little strange. Even if you don't have a point and click interface for the weapon, a lack of jumping is a little frusturating.
2) Crouch? You can't even shoot and crouch at the same time. I don't get it.
3) The boss, or whatever you'd call that thing that lasted 5 seconds was pretty weak. Although I compliment the change of style.
4) Everyone has said it, but...when zombies pop up right next to you while you are being cornered (you can be cornered in 2D...), you lose or react with wild grenade fire and running.
5) For some reason I couldn't buy the last upgrade to my attack strength, the price was 5000 or something and it just said full power when I clicked on it.
6) Is there supposed to be a delay after using the grenade launcher? This is just a question not really a complaint, because it might be too easy if you didn't have a delay.
Despite my list of concerns, which I tried to be nice about. This game has a lot of potential for growth and betterment. I do like the simplicty of having one weapon, but I am pulled at the thought of having more variety. I would like to repeat that I liked it, but I should re-emphasize that it can be improved upon.