One suggestion:
In the inventory, when I select a character I'd like it to auto-select the appropriate class on the right. This would speed up each time I equip items by about 50%.
The rain on the 2nd final boss is just annoying; artificially making the level harder, not by mechanics but by messing with my eyes and lagging my computer.
Something about the jumping feels really unnatural. It's too difficult to hop. You have to wait too long after landing before jumping again. Difficult to judge how high you're going to jump. Neat concept, though.