Bugs and difficulty
I have got to wave 45 on level 5. This is as far as I can take it before those damn huge flying helicopters with about 25,000 hit points each take me down.
My maze at that point had four red DCA in the middle and five purple ones around them. Then Red Sniper towers about ten and red SAMs x 5. The rest were mostly yellow or gray vulcan towers.
It's impossible.
It's even worse with the cash bug, as I have lots of cash sometimes that disappears.
Please make more tower upgrades, or allow the player to have more impact on the game, for example the player should be able to hold one alien at a time with the mouse. Doing that means it can't move, but you also can't place turrets.
Anyway, meh. I really wanted to win.