I like it! There's lots of stuff that could be easily expanded upon. Only criticism I could give is that it can be hard to see what you can and can't stand on. During the boss fight I literally said out loud "Oh you can stand on that." I'm not an artist but I'd recommend either using brighter colours for platforms, or what I'd think would be better, giving platforms a thick black outline, like the characters. With that said I tend to like games based on how much my hands hurt after playing them and this made my arms hurt like hell.
P.S. I love the uppercut.