Honestly, it looks like you downloaded some visual game creator and made this in 10 minutes. I have nothing against that, but the game isn't even enjoyable. Look:
1 - Too slow paced;
2 - Controls/dynamics suck;
3 - Unpredictable collision check. This means that you have to always target the exact top of the every enemy if want to guarantee that you won't take damage. With time, this can annoy/frustrate/stress the player. We play games to have fun, no to be stressed;
4 - The "take damage and get pulled back" things is totally annoying in ANY platformer; try the "temporary ghost" approach next time, or maybe the enemy explodes when it damages you, or maybe you could attack the enemy from distance. Do anything, but don't do this poor mechanic again. It rarely fits in a platformer and definitely doesn't fit this game.
5 - The challenges don't match the poor controls;
6 - The tunes simply don't match the game;
7 - Colliding to the sky?! Seriously? The top of the visible area isn't solid, unless you place something there to indicate that it is. I died many times trying to jump higher than the "screen". Colliding to the sky?! argh!
It looks like a first effort. Take this as constructive criticism.
Thanks for the effort. As you can see, if you simply tweak some variables in this game it can become much better.
Thanks for spending the time to give detailed feedback. I will say though, this was not a slapped together 10 minute job here. Roughly 3 weeks went into this game. I made the artwork from scratch, programmed all the enemy movements, and designed the levels by hand. I did not follow a pre-made template even if that would have been easier and faster.
As for the feedback, I will keep it in mind for future games. A lot of the problems you mention are things that were present in the original Mario games which I was attempting to emulate. I did try to do some slight modernization by having lives activate on the spot, and making pits only do damage instead of instant death.
I considered allowing "Ghosting", but I was concerned that with the character already reviving instantly, it would allow players with several fairies saved up to just run through the final level without avoiding any of the obstacles or enemies.
Again though, thank you for taking the time to write detailed feedback. I do appreciate it, and will follow it more closely in future games.