This game has great potential!
I really loved the graphics style of the game. Simple, but cute and effective. As for the towers... what I tended to do on any level with ghosts would be to do sleepers and eye towers. Sorta like (with S being sleeper, I being eye):
S SS S
S IS I
S SS S
S IS I
S SS S
This allowed me to catch pretty much every enemy with little difficulty (the real difficulty, is knowing how to put what blocks when and where). Wrath and the survival block effects made me rage face at times because of the fact they kept targetting the blocks right at the bottom of a stack, so I'd have to get rid of the entire stack to fix the one broken block. >:O
Otherwise, I just replaced the eye towers with sleepers. And sat there killing everything. I'd recommend giving some more variance in the gameplay as well as a bit on some of the blocks (the magma block was completely useless. Curse block works far better as it has a bigger range.) I'd recommend to folks who want a challenge NOT to get the doll damage upgrade or missile upgrade, but the other ones (except survival mode one. Don't get that, as you get it at the end of the game anyways).
All the same, I like the game (AND that you made it completely FULL GAME without having to do the whole 'Use mochicoins' or whatever to buy content or going to X site to get to play all the levels. Kudos to you!). Hope you continue to make more for newgrounds.