For those complaining about control: I haven't tried the challenges yet, but I finished career mode w/o giving any orders at all. Just make sure you're using the best stuff available and max out for the weight class.
Well it's definitely possible. Perfect finish on hard. As Massbeat says: bombs and boomers (though he left out the occassional spike spam).
Fun game. Actually makes you use a variety of towers to win. And I like games that don't have the numerical backend right there for everyone to see. Feels much more organic, less like I'm minmaxing a D&D character or something. Nuts to the haters who want to see "20% damage increase" and "pops exactly 3.78 bloons/s". Real life makes you figure out the numbers, so should games.
One pretty neccessary tweak, though: take monkey tails out of the hotspot. I hated having to wait for a monkey to turn before I could put a new tower next to it.