So right out of the gate, I want to say I completed the game, it was engaging. From a gameplay perspective, as others have said I think the controls could use some tweaking (with platformers it is hard, I am in the same boat and need to tweak my controls as well). However, I really liked the idea of changing the effects in play based on whether the player had been hit. I think it is a super cool twist and I enjoyed it, and the challenges/perks it introduced. I also want to say I really really like the checkpoint system. I think the checkpoints worked well, and it was smart to activate them if the player gets stuck on a spike. I also really liked the visual effects you had when the player is respawned on a checkpoint, it was a nice touch.
Regarding the way the game looked, everything was very clear and it was never hard to understand what was going on on screen. It was also super helpful that you provided information on what current gameplay modifiers were active. The game also sounded pretty good, minus one odd transition, but seriously everything that needed a sound had one, and that further helped make the game clear. On the presentation side I really do not have feedback, it was all very well done.
I am very impressed that this was built by one person and congratulate you on a job well done. thank you for sharing, I had fun playing your game.