Overall it seems fine for a beginning programmer, but there's lots of room for improvement. It could definitely use a preloader screen like the game description mentions. The gameplay is very basic, just top-down shooter with a small empty field where you kite the zombies around. There's no reload button so you have to intentionally empty your gun to reload. The story doesn't seem to be interactive (I always prefer to have the story be revealed in the gameplay rather than with text, and having the text presented as sort of a side note on the main menu detracts even more than if it were at least presented between levels or smth) or compelling like the game description says, although I haven't gotten that far into it. The graphics are pretty basic. Sound worked on Chrome and Firefox but not IE.
That said, if you're new to game making, then making a functional top-down shooter is a big first step and would let you add on more stuff to the platform you have, depending on how flexibly it was programmed. Most of the top-downs I've seen that I liked involved running around in a maze and solving puzzles as well as killing enemies (along the lines of Outpost:Haven). Which might be easy to do with the existing code or might not depending on whether you're locked into having the entire playfield be on the one stationary screen. Or if you want it to be more battle-centric than exploration and puzzling, then I would suggest making enemies with different behaviors that call for different approaches to kill (maybe you've done that and I just haven't gotten far enough into the game to see it) and giving the player different weapons with different mechanics throughout the game. But see if you have the same issues with no sound in IE because that's kinda a big bug if it's not just something screwy with my computer.