Great visual and sound style, interesting idea behind the implementation of "only one", being the only one input at a time.
One downside is beyond the means of showing where to jump, coins felt a little unnecessary (to the point where they weren't even tracked). However, they did feel satisfying to collect, so having them serve a purpose beyond that would really enhance the gameplay. Movement also seemed a little slow and heavy, but that is easily gotten used to over the course of the game.
Had a lot of fun, played to the end, and was willing to play more.