What an amazing game! I played it right through and adored the polish put into this.
Aesthetically it's right up my alley. The minimalism and colours worked great. The little things like transitioning on level reset/advance, screenshake and particles are all tops.
I loved the sequencing of levels and introduction of new ways to navigate the levels. Funnily enough the hardest level for me was "Gah"!
In general I feel like the bullet collider could've been a bit more generous towards the player to provide more cover. Or maybe the laser's collider been a pixel or two smaller.
I would've loved R being mapped to restart, just to shave milliseconds off my retry and somehow fixing that dreaded Unity 2D platforming issue of sticking to platform edges and not being able to jump. Perhaps a physics material would fix that but in my experience it doesn't always feel right.
I'm very envious of your game, I can't wait to check out your code to see how you did things.
Congrats!