I understand what Qweston is thinking, but I think a better approach would be to be able to select multiple towers at once then upgrade each by one and the cost be the total value, that way you could limit tower upgrades to specific ones to maximize damage in some areas while leaving others alone as guide lanes...
one tiny problem, I keep randomly having my ship jump to instant death after accidentally brushing against an obstacle near the top of the screen, it happens on the bottom too but near as often. happened about 5 times in a row now in the end of time stage absolute zero. please look into this
48 was harder than 50 I think, took me 30+ for 48, 9 for 50
also to mr 753398445a, it's not that you are awesome, but rather you actually died before level 30?
umm...yeah...a destroy/sell option would be nice, you CAN over load your map area and get stuck on a level, unable to win, unable to die...happened to me on like the 5th level, built up to win ended up stuck
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