My man, this is a cool twist to a tower defence game. I didn't get too far yet to make a complete review, even at easy mode the game is quite difficult. But it seems doable, and is surely a challenge.
A bit more tutorial would be very nice too. In the beginning, I missed the spells and how to buy it. You're too focused attacking those enemies to realize you just have to hover over one of the spells to see the price and buy it.
I agree with TT : I really missed the reset button. That costs you half a point, but since we round off, it's still 10.
Be sure to place your cannons high enough (watch out for air units) and in the center of the tower. This avoids them getting destroyed immediately when it really starts to matter.