This reminded me a bit of "Kingdom Rush" from back in the day, but in reverse.
The graphics are solid. I love the style you chose for the minions you spawn in. The round based combat is also a nice touch, as it kinda reminds me of waves in a TD game. I was a little confused how to place the characters at first, and the lancing enemies seem to be the most effective for your money as the others kept getting cleaned up too quick.
Great entry, I think there's a lot to expand upon here.