Why does someone...
... buy a Flash game that is free to play on the web? In fact, I could probably get my hands on your SWF if I really wanted to. Not to mention that, in my opinion, you are completely over-estimating the amount of interest your game will draw. It really isn't that good. A few things that could have improved:
1. Graphics - they appeared to be screen-shots of actual photographs of nature back-dropsand textures. Pu this up against STICKS, and you've got less than a winning combination. Plus, there wasn't any variety in the levels themselves really. A straight-piece of land and a couple of inclines. No trees... in fact nothing that would have been present in a real-world experience. And the zombies really needed to be something other than other stick-people with different colored heads. That just made it feel like next to no work was put into this.
2. The physics model used was strange. When I jumped against the "walls" that held me inside a level until I killed all of the "zombies" it kind of bounced me off of them. That, and the character was able to jump between 5 and 6 feet into the air... which ended up being almost half of the height of the game itself with the Stage-size you chose. It just felt odd.
3. Give the player some indication that he has been hit other than just decreasing health. Make the character graphic/animation flash and jump back or something. It is also always annoying in games when you can just stand on-top of enemies and take continual damage until you die. And the enemy wasn't doing anything but trying to walk by me with his arms out... no attacks or anything that would really have made me sustain damage.
4. The music didn't fit. It was kind of upbeat and almost funny in a way. And that makes me think of another thing on the lines of the graphics... the backgrounds were too bright. When dealing with zombies I usually think of darker, more foreboding atmosphere conditions... not walk-in-the-park style forests and ski-slopes.