Try to make the background more different than the foreground. For example desaturate it. At the beginning I've had a bad time realizing where can I jump and where not.
Also jumping on key "just pressed" would make more sense when jumping is so rare and the longer you're pressing the key makes you jump more. Often times I wanted to make a long jump and the second jump triggered right after landing.
Anyway I like the idea and art is really pretty!