The art that's there is great and clean, and is pretty well designed. And I agree with others that once the main character is in place it'll feel much better, because playing as a cube doesn't feel so good. Also I couldn't find a controls layout for keyboard, but that's not a big deal, I kind of bluffed my way through it. Combat feels good and snappy, but I just wish there was more!
Kinda wish there was some sort of notification when you beat the demo, cus I wondered around for a couple minutes trying to figure out what to do. And then when I entered the two balls room again the green tree door thing appeared again and I couldn't get out.
But great work, I enjoyed playing it. Keep it up!