I like the art.  It starts off very slow and takes a while to ramp up.  There's not much to do once you've filled your screen with towers.  After filling the screen I just let this run while I did something else, just to see how the difficulty would raise.  I lost my first princesses after about 3 hours, having collected 26k souls, because the density of the horses just overwhelms the speed you can shoot at them, and they zoom right by.  I lost about 30 minutes later, with 35263 souls

I like what you were able to do in 3 hours

Nice art!