didn't like it very much
I played on "medium" which should be a fair difficulty. However, it is apparently _impossible_ to defeat the first ground boss on medium. What gives the most damage per second at that point is a couple of upgraded flame towers, plus a frost tower to slow down the enemy. With all three towers hitting him, the boss still had more than half his original health left, even after he passed the towers twice.
I call foul. In a good TD setup it should be at least _possible_ to kill every enemy if you play right. If you have to play on "easy" for that to be possible, that's just insulting.