Architect: How should we design this castle so that it will protect the king?
Apprentice: I know! Lets put a tall stack of explosives right in front of the castle with a short stick on top so when the explosives blow up, the stick will fly through the window and hit the king on the head!
It seems possible for the money variable to get in the negative. (You can use "powers" even if you have no money) If you attempt to "shake" the creeps to death, (The third power option) they will not die even if you use it several times.
The bosses seem to have too much health. I couldn't kill any of them. (It seems the only way to kill a boss is with an atomic bomb) I noticed a glitch with the ice towers... they caused the creeps to stop for a few seconds, and while they were stopped, no tower could fire at them! When I tried to place a tower to close to another one, there was no error message. It just wouldn't allow me to place it there. One thing that would be nice to add is if you could see the range of your tower to optimize tower placement. It would also be nice if there were tower upgrades. (More damage, splash, faster shooting speed, ect)