Too frustrating to be very fun.
I think the biggest flaw is the graphic design. An extra color would be really nice. You only have two colors, but even with just two colors there is seemingly no consistent color design. Platforms, items, enemies, hazards, foreground and background elements all use both colors in the palette. Compare to something like Downwell, where the player, level, and miscellaneous objects are completely white, enemies you can stomp on are white with red tint, and enemies and hazards that cannot be hurt by stomping on them are fully red and filled in. This lets you instantly understand what obstacles are coming your way.
The next problem is with the way the theme is implemented. I think it works well enough, but with how much your view is obscured, it makes going through levels a matter of trial-and-error. I think it's at odds with the fast-paced mechanics of the game. I'm not sure if there is a good way to fix this with this concept, this may just be a thing that will bother some people more than others.
The third thing is the design of the levels. Most of them are okay, but there are some that start you off on a disappearing platform or immediately next to an enemy which can lead to some cheap deaths when you're trying to just look at the level for a second (which is made harder by the lack of consistent color design). Not only that, but having to make blind jumps to invisible platforms is really annoying. They could at least pop up occasionally so it's not completely trial-and-error... Finally, the exit of the level is somewhat unclear. You go off usually the top end of the screen, but sometimes the sides. Either way, there are times when there are no walls despite the fact that you can't actually exit the level through that way.
The fourth thing is with the general game feel. It's nice and fast most of the time, but maybe a little *too* fast. Springs and dashes launch you instantly at a high speed, which can be difficult to track due to the low resolution and obstruction of your view. This problem also happens when climbing ropes. Your momentum is conserved when you hit a rope, whether or not you are holding up or down to climb, so there's no real indication that you even grabbed a rope, not even an audio cue. Your sprite also doesn't change on the rope unless you are not moving horizontally. It interacts weirdly with your momentum and makes the climbing feel... bad.
The fifth and final problem I had was the lack of in-game explanation. This is rather minor, as you could just read the game description on this page, but the description is pretty lengthy. This is evident right on the first level, where you are told that you can press Z to jump, but not that you can climb, or that the thing hanging from the platform is a rope that you can climb! Then, in the next level, you are told "X to dash". This one might be a language thing, or maybe trying to be too brief in your description, but most people would associate a dash with something that moves horizontally. However, this "dash" only boosts you upwards, and isn't aimable horizontally at all, so you might as well just call it a double jump. Two other things with the dash that you aren't really told is that you lose it once you land on the ground, and that collecting one will destroy the enemies.
Sorry to be so harsh on your game, it's clear you put a lot of effort in it, but it didn't work out for me.