Geometry Wars huh?
I've seen Geometry Wars clones before, none of them turn out so well. Geometry Wars is designed to be as frantic and as fast paced as possible. You took that away completely by involving ammo. I would like this game at least 5 or 6 times as much as I do if you removed the requirement for ammo.
Also, I think you should make gun powerups that appear about every 40 seconds. Powerups like double, triple, and eventually quadruple shot. Then I think you should put a ton more enemies on the screen at once early in the game who are all 1-hit-kill.
I also hate games where, when you touch the side of the screen, you teleport to the other side. Just put in some walls man :P
Summary:
Take out the ammo, put in a ton of enemies, a ton of powerups, and walls on the side of the screen. Then put in a quality option and all's good :)
p.s. maybe make it a little easier to control where the player moves too.