Unfortunately it suffers from the same kind of balance issues that basically every tower defense has, where some of the towers are totally useless. Every single level can be beaten by some combination of lightning/saw towers, and every slot that you use for a machine gun/cannon just makes the level that much harder
Guys, the payment for premium upgrades is a decision on the part of the developer, not on the part of kongregate. No matter where you play btd 4 you have to pay for the upgrades. Don't get pissed on kong, get pissed at the developer.
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 "Walkinator"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
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