Rewinding to make obstacles go away is simple, but fun with your level design. When it was over, I was hoping for me. I'm a WASD-user, so it took me a little time to adjust to arrow keys (I found it too hard to move and rewind at the same time with WASD). When using WASD, my right hand is completely free. If I have it over R, it blocks WASD and jump. Maybe The mouse button or enter or < could have been used to rewind as well?