Just sent you feedback on that form, but adding here some more, just to emphasise a bit on one thing.
But first, you had one question of "would I download this from steam for free", I Answered this "no", but this will give you wrong imporession. Point for "no" is, that I dont look for free games from steam, I only buy games.
Idea is that in my mind, if someone asks money from a game, he probably made sure it is of good quality enough. If someone is giving away game for free (unless it is to promote the full game, like being a presequel for the full game), then I dont trust it is necessarily done to the quality, and hence I am not looking for free games from steam.
However, if your question had been "Would you buy this game from steam", to that I would say "maybe".
Thing I want to emphasise and hence separately write here too.
Your game is good as it is. I enjoyed playing it, I played through all the four levels, and would have liked there those "coming soon" 4 more levels to having been too.
However, even it is fun as it is, it however did feel amateurish all along. It felt bit clunky, as in how the ball came back, movement didnt feel Mario smooth, but felt like amateurish too, especially on moving platforms you notice it, since you sometimes get backwards, because you speed up too slow. That you move on moving platforms backwards, in itself is slight problem already, but due to movement not being satistfying, but speeding up too slow, it adds to the problem more. If movement would be feeling smooth, speeding up faster, then moving on platforms backwards wouldnt necessarily be a problem, and you could even ignore that problem.
Basically, just add to the game all kinds of bling bling, and this game can become really good.
Things like when you run and then start running towards other direction or simply stop movement, make breaking animation.
When you kick the ball, add there some effect, like flash the ball or something.
When kicking harder (keeping left mouse button down) add there even stronger effect.
When enemies get hit, add some effect, all around all kinds of effect to make player feel more. More effect to picking items etc.
It is a really good game, but it needs more bling. Or, as many call it, Juiciness and Game Feel.
Here are links to two videos to show you about the Juiciness, hope these help: