Very impressive.
Aesthetics are great. The game manages to look amazing despite everything being composed of cubes, the music fits very well to create this really chill mood. I also think it was a good idea to place HUD elements on top of the player, instead of the edges of the screen.
The mechanic of dynamic damage/speed tradeoff is really interesting and I don't believe I've encountered it before and I like how your design accommodates different playstyles.
Unfortunately, I didn't manage to master either of the playstyles, since the controls felt awkward to me (I used a mouse) and I didn't get used to them even by the time I completed the game. Additionally, sometimes when an enemy exploded the game froze up for about a second, which was disorienting and made it hard to properly take advantage of the explosions (though it might well just be that my PC is too slow). Another gripe I have is that it was frustrating to get thrown back by an explosion into the previous stage and, after resetting, still appear there instead of being returned to the latest stage (though maybe it's my just punishment for being bad at the game).
It's nice that you thought of and actually managed to implement a proper intro and an outro for a jam game and I liked how both are delivered.
Overall, I must say your game is a highlight of this jam for me. Extremely well done, especially considering you essentially did it alone.
And it has a Linux build and is open source.
Wow!