Hey brotha! I just played through the first world of this game. I had a lot of fun! A few suggestions in case you plan to update this game later on:
1. This is a bit of a nitpick. I think it'd be cool if in the "How to Play" page, you let people use a button on the controller to exit back to the Main Menu, rather than having to use the mouse to do so.
2. Jumping is overall good, and the levels are designed well around the jump height, but the jumping could be a bit more fluid. If you want the jumping to feel top-tier, you should make it so that rather than having the character jump a fixed height every time, make it so that tapping the jump button without holding it only makes the player jump at a small height, while the player has to hold the jump button to jump at the maximum height.
3. Having a sound effect when jumping on an enemy or sliding through it would make killing enemies a bit more satisfying.
4. There was a glitch at the end of the first level. I touched the exit door from above, and it caused the character to disappear without going to the next level. I'm not sure if this happens in later levels. Entering the end door from either side works fine though.
5. How many worlds are there in total? If there are more than a few worlds in this game, you should add a save system so players who make it past the first world can exit the game and later continue from where they left off.
With all that said, I do enjoy your game a lot, and I will share it on Twitter. Hopefully I can get others to try it out. Keep up the good work!