Neat, I had a good time with this one. I like that I can play the same thing twice from each perspective, and that the role-reversal actually takes place as I play, rather than just as the basic premise of the game idea. Cute art too, I like your sprites :)
I wish that my actions from playing one side carried over to the next round as the other side in some way so that I actively have to think about the role reversal as I am playing.
And I think it's interesting how the typical tower defense ways of making levels more complex only really apply to one side. Adding more paths means interesting choices for the defender but it just means I choose the weakest link as the attacker. I wonder how more complexity could be created for the attacker too.
By the way, when I won the attacking side on level 3, my game stopped with an eternal freeze frame.