Nice potential, poor balance. You level up way too fast, and then it's the same over and over again. Suggestions:
1) Give a discount on upgrades, ie. purchasing a better gun in the same class
2) Allow weapon switching with 1-9, display numbers and weapon names at the top of the screen
3) Do something about the lag, please. The graphics are nice, but they come at a heavy cost
4) Way more expensive weapons
5) More diversity between zombies, like different moving patterns and resistance to some types of attack. Maybe there is already, but I don't notice it
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