Great! I could also imagine to add SPACE for jumping. Or if you need more: R,B,Y to activate the red, blue and yellow switches... With all of this you could probably design quite a few interesting levels. The more items the less straightforward it gets, since you don't know anymore what you should get next, while having more options to do something already. (If you continue this project and like to have me contributing level ideas, just contact me, e.g., on Twitter or with the form on my webpage. That could be fun. :)