I think you should create some sort of survival level were you just kill your enemies for fun and its endless it will only end if you die and plus so you can have lots and lots of gold after playing the survival mode to beat your score
There should be more upgrades for the base and especially for the turrets because we dont want to get a unit lost in the mission and while upgrading every upgrade should have a change on the turret so it can be more cooler but still its a very cool game 5/5
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