So you pretty much don't need any other tower than the heat wave tower (the more powerful laser tower or whatever it is called). They basically one shot anything, and if it doesn't, the penguins get stunned and die anyway. Lot of towers to use, but no point in using them.
Oh, and to add on to my previous comment, even just scrolling down the screen to look at the comments, causes the towers to either stop firing, or slow down on firing.
Definitely reduce the amount each tower costs, and as it stands, you have no LOSS. You can sell, resell, buy and rebuy things over and over again with no loss. You get everything back. Reduces the difficulty of the game GREATLY.
The number 1 spot person "Boratiscool" hacked this score. His Idle time comes out to something like 8 days, and this game came out yesterday on Kongregate.
@spider, the reason you can't go into some places is because the pieces don't match up, if you could go anywhere at any time, the game would be too easy.