My opinions on this...
It's a brilliant little tower defense game, but I'm afraid what detracted from it was the factor that one of the achievements, the pyromaniac one, does not trigger at all. I went all the way to round 12 (where you will die, regardless because you have no air killing turrets) and it just did not work. That achievement needs to be fixed along with any others... other than that, the difficulty could do with a big tone down as even on easy, you just start to die really quickly at round 11 onwards.