This is such a cool idea! I love the idea of momentum being tied to damage, and it was really satisfying to get up as high as possible so I could smash down on an enemy. Music and sound effects are great (other than the bug you mention on the page), and the retro graphics are great. I like attack and movement being tied to the same controls, too.
The movement is also easy to pick up on, and feels really good. I think you've got things tuned just right.
All-in-all, solid jam entry, and it would be cool to see it fleshed out a bit more. I could imagine a full game with these mechanics and a mix of platforming challenges and combat.
Great work!