First thing's first: The choices you added in your game such as deploying cheap troops or mines anywhere makes it easy to be exploited. I think you should work on making the costs for such troops much higher. Other than that the upgrades menu is boring and hard to fill, also the things that have already been said, you can spam the beggining area with snipers and mines and zombies will never reach the end. It's just a boring wait until they are all dead. Fix the bug where you can use hotkeys to deploy things even if they are on cooldwon and make more speeds for the game (it takes way too long) The graphics are decent, now invest time in game mechanics/gameplay.