The perfect cure for too much Xeno Tactic :)
It's probably not the be-all, end-all defense game, but it IS an excellent game that goes down very smoothly. You can catch your breath and build after every wave, each level passes quickly enough that you don't feel bogged down. Things never get impossible due to enemies having too many hit points.
I used clusters of tack towers in the corners, followed by a few peircing dart towers to take out anyone who got through. When the black balloons started showing up, I built a second group of tack towers, and that was pretty much enough to see me through until it was time to start building Super Monkeys. And of course, once I had one up, I could easily keep adding more. No need to upgrade their range, because their range wasn't an issue, just their stopping power.
Freeze/Bomb combos were never of interest to me, so I wasn't bothered by the white and black balloons. I think the strategic importance of them would be improved if there were some balloons that could only be destroyed using freeze or freeze/bomb combos, but you might need a bigger playfield for that. That's something to look into for a sequal.
Ultimately, what you've done here is use a fixed number of enemy types, whose charecteristics do not change between levels. That does a number of subtle things to the gameplay, or should I say it prevents a number of subtle problems that can arise in games like Xeno Tactic and Tower Turret Defense or Onslaught 2. It does make the game easier, but only because understanding the mob you see before you is simpler and more intuitive.
Less obfuscation = less confusion, = happier gamers. :) I'll admit there isn't much replay values, but this is a good, solid defense game, and like I said, it goes down very smoothly. Keep up the good work! :)