It's not terrible, but there are really a lot of things that need improvement. 1) The speed after losing catapult/booster propulsion is way too slow. No one likes/has the time to watch the character crawling across the screen for an inch a minute, let alone watching that repeatedly. 2) The first rocket upgrade was a bit absurd, especially that it turns all the catapult upgrade into waste. 3) Armor and durability are essentially the same upgrade. 4) After a certain point the game pretty much doesn't need any controlling. As I'm writing this my zombie is just grinding by itself since the input/output ratio is minimal.