terrible
the graphics were bad, they looked like they were made in ms paint, i suggest you get a free tool like gimp to make the graphics.
the parameters given were limited, you should be able to make the zombies die in one hit, or make no extra ones appear after levels, and adjust the defense upgrades, possibly adjust the amount of money per kill and upgrade costs.
the zombies went to where they spawn whenever i shot them, making killing them over complicated, my gun did not shoot far enough to hit the zombies most of the time, my guns fire rate was random, and combined with the fact that they threw grenades at you, and you have an almost impossible to play game.
my summary:
graphics: 0/10
gameplay: 0/10
customization: 3/10
overall: 1/10