I really like this one. The enemies are bizarre, but neat, and there's a lot of thought put into the level design itself. The powerups do feel meaningful too, and it feels great being able to get past obstacles that used to be a pain to avoid. With that said, there are a few small issues that I'll echo.
Getting hit can sometimes feel very punishing. There were times where I would get hit by a brush, knock back into the air, and then fall onto the brush again to get hit, over and over until I died. Knockback is simply too large, and the lack of invuln to getting knocked back again means you can get thrown way back or take a lot of damage for one mistake. I gather this is why you added the healing ability. I do like the touch that the upgrade board 'hurts' you so that you can recover again.
The water rising puzzle feels like it is a bit tight, probably because you need to double jump at the very top of the first jump arc to clear the last platforms and reach the lever. It also wasn't clear to me that the reason the music changes was because water was rising until my first death, although it was very nice that it respawns you at the bottom to try again.
The jump sound is a little too...Idunno, squeaky? Maybe high pitched or loud? You get used to it, but it was one of the things that got on my nerves at first.
I think the button prompt to activate checkpoints only shows the controller button, and not the keyboard key. However, you do list the corresponding buttons on the page, so this is minor.
I forgot I had a map until the end, but it is a very nice feature. In a way, that's a sign that the level design was very clear and not repetitive, as I didn't need to use it much to figure out where to go next.
Despite my criticisms, I want to reiterate: this is REALLY good. Keep making games!