The combat shotgun fully upgraded with increased radius is totally broken. Almost no monsters get a chance to even appear on the screen. I outdamage the Gauss rifle because the shotty hits half the screen at once.
The unnamed sniper towers are way too good. I can defeat the very last level by building nothing but those near the spawn point. The cheap towers are useless, and cannot be upgraded.
5minutes: The problem with this td game (which is otherwise very well made) is that you're going to have difficulty achieving a good balance in difficulty. The reason for this is that you're using a roughly linear damage for money ratio--that is, it's just as effective (perhaps more so) to amass more towers than it is to upgrade them (with the exception of poison/fire). I suggest switching to an exponential formula.
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