This one caught my attention a while ago but then I forgot about it. Glad I did find it again!
The idea and art is really nice. One immediate complaint I have is that first enemy slimes took 7 shots. There should be a variation that takes 3 shots max, even if just for fist wave.
Boss 1 didn't feel too interesting as all its attack would work more or less the same on flat terrain. Other 2 bosses however did take advantage of world being round.
ALl in all this was pretty good!