1st: It would be nice if the music was muffled/changed when in the shop and research window to indicate the game is paused

2nd: some upgrades straight up don't work, the auto fire for the main gun and the global turret range from the radar don't appear to be working. Either that or they're explained very poorly. 

3rd. Remove a lot of the upgrades levels from the research tree. Not only would it make balancing easier it would also make each upgrade feel a lot more substantial

4. the jumping zombie hitbox feels a bit off  

5th. some boss/mega zombies would provide a good challenge