Love the music and the artwork. The game was a little slow to get going, could have done with a triple speed button, not just double.
Also the pricing of units was a little odd, spamming the weakest unit is the most cost effective thing to do. As you get more HP/Attack per gold on the 8 coin unit than the other two.
1st Unit has 10 attack/HP for example and costs 8 gold.
2nd Unit has 50 attack/HP and costs 50 gold.
But 8*5 is 40, so if you buy 5 of the first unit for 40 gold, you're getting that 50 attack/HP anyway.
The difference becomes even larger on the last unit.
A couple of balancing tweaks and this is a solid framework for a game.