I just finished the game and I really liked it! The movement feels really good and the powerups are very fun to play with! The narrator dialogue was fun to read throughout the game and well presented. The visuals are minimalistic and clean. They communicate the mechanics well and look slick. Level design was good and everything felt challenging but not impossible. There was a major difficulty spike at the very end of the game during the boss fight but of course that's to be expected.
There are some improvements to the game I think you could make: Firstly, and most importantly I think a major positive addition you could easily make is to add a button to let you quickly restart from the last checkpoint. The lava looks cool but seeing the short animation of the player sort of sinking in over and over can really add up to a lot of time the player lost when they could be playing. This is further compounded when sometimes the platforms are way higher than the lava so you have to wait until you fall all the way down and then watch the death animation. Another improvement that could easily be made, in my opinion, is if you did not use a default Unity graphic for the boss health bar and the progress bar during the boss fight. To other developers that have used Unity it sticks out like a sore thumb and it also just doesn't match the polished look of the rest of the game at all. Some people might not notice it but just a simple long rectangle would look much better than one of the low-res Unity default graphics. Walljumping on the blue lined platforms is fun but hard to do a lot of the time. Its not finicky exactly, I think its consistent in how it works, but it just works in a way I wouldn't expect without thinking about how to do it. Maybe that one is just me though.
I also did encounter some small glitches while playing: The player can't stand on a lot of the vertical platforms without getting awkwardly slowed and then shoved off into the lava. It feels like gravity increases when the player does that. I assume this was intention as it only happens in places where it seems unintended for the player to stand on top of these platforms but the implementation is very awkward and it seems a little glitchy. When I finished the game the final level with the boss had no completion time so I clicked on it thinking maybe it was an extra secret level. It was just the normal final level but the darkness didn't appear and the boss appeared at the end of the progress bar at the bottom. When I clicked the button the lights suddenly went out and it progressed normally. I went back to the main menu and the ominous boss sounds continued to play along with the main menu music though.
I know I probably wrote more constructive criticism than positive feedback in this comment but I genuinely like the game a lot! Its very fun and it looks really polished, especially for a beginner!
Good job! :)