I know it's just a demo but I believe you could avoid and learn from some of the common design flaws in platformers.
Design (2/5 platform) - The game just has all the mechanics of a very basic platformer. The UI was a little amateur as well. Lastly, you should consider adding instructions, never assume the player knows the buttons for the game.
Audio (3/5 backgrounds) - I really liked the background music and I think it fit well with the game. However, there wasn't any audio anywhere else like in the title screen or any sound effects when dying.
Mechanics (1/5 jumps) - As I mentioned, you have the very basic mechanics. You need your game to stand out from the whole ocean of platformers already out there.
Art (1/5 crosses) - I'm sure you can do much better for all the art in this game!
No progression (1/5 balls) - It got boring pretty quickly for me. The game introduced two new enemies but then it lost the challenge. I suggest you make it harder over time for the player by either adding more of the initial obstacles introduced or introducing new ones. You should also add some checkpoints.
Cling (1.5/5 walls) - I could cling to the sides of the platforms and rise anyway which I doubt is meant to be a feature.
Shock (2/5 songs) - I like the background as I mentioned earlier but it gave me a huge shock at the start because of how loud and sudden the beginning was. Not to mention, I didn't expect there to be any music since it was absolutely silent before that.
You have the basics down, now its time to make your game stand out and polish it to perfection. Good luck!
Jump around for yourself right here: Madness Adventure DEMO