Given these comments, I feel like the only one who didn't really care for this entry. Being a platformer, there was a lot of jumping around, timing movement and jumping with obstacles (spikes), and finding checkpoints, but that seems to have been all of the gameplay there was to this game. There aren't any decisions to make, no creativity on behalf of the player (other than perhaps finding new routes, but there aren't many opportunities for that), few mechanics to work with, only timing your movement to run from safe-spot to safe-spot before spikes kill you in-between.
I ran into several glitches while playing the game that definitely hampered the experience with unnecessary deaths: the spikes that come from floating ceiling pieces can still kill the player if they walk against the side of a wall that contains the spikes (example after checkpoint 5) (check player hitbox and make sure it's not overlapping into the wall when moving against the wall), the player can clip through some wall corners while falling (example after checkpoint 7, when falling down to the first challenge area after checkpoint 5) (not sure what to recommend to do to remedy this one), and lastly the checkpoints themselves can be very glitchy at times, sometimes spawning you about 5 blocks or so above their location, and they apparently have a hitbox you can jump through and stand on top of (make sure they only act as a collider, unless this is intended).
The checkpoints that are in areas that will kill you are just plain frustrating because you cannot control when you respawn, so you may sit there and wait until you die 2 extra times before you have a chance to move. This would be much less of an issue if the game waited until spikes/blocks were not literally directly in your hitbox when you spawn, and would still retain the challenge of some of the checkpoints will kill you if you wait there too long.
The camera can take a long time to pan back to the player if the player dies a far way away from their last checkpoint, which is frustrating when you know your next checkpoint is a ways away and you need all the time you can get to make it to the next checkpoint. It'd be nice if the camera would either snap back to the player, or move faster back to the player if it knows it has to move further. I can't tell if you already have a system like this in place, but if so, then reducing the time it takes for this snap-back to complete would be helpful.
Movement felt clunky to me, like the players movement was inconsistent and was jittering a lot, but after checking the game again, it seems that this is an issue with the camera snapping to the player at about 10-20Hz. It appears this camera snapping is handled via FixedUpdate, and would look a lot more smooth if it were instead on Update.
Lastly, I just didn't feel that the light/power/time between checkpoints ever gave the impression of being power, and this never gave me the feeling that I was Running Out Of Power. Besides death and slightly dimming the screen, power didn't appear to do much anything, so rather than feeling I was running out of power, it felt more like I had an obscured timer ticking down that displayed a (presumably empty) battery upon death. Perhaps if the light from the player was a bit more noticeable (it appears to be much more significant in your screenshots than in the actual game) and having that be reduced closer to death, or perhaps making the screen dim much more significant would better convey to players like myself who never got that intended feeling.
I'm glad you do still have people who enjoyed it, but I really didn't care for it in many ways.
tl;dr: Didn't enjoy the core gameplay and felt it didn't well fit the LD39 theme, but explained my several other gripes with the game and possible fixes for many issues and some bugs.