Level 12 was my favorite; it took me a while to figure out, but the progression of slowly figuring out each section of the solution, and then finally watching the chain reaction, was so fun. Even when I was stumped on a level for a long time, I never felt lost on what to do. There were always a few microbes placed in odd positions that made it clear how the chain reaction was generally supposed to go; then, it was just a matter of solving the Sokoban puzzle to get the microbes in the right order - great level design!
My only critique is that I wish I could hold down the movement and rewind, similar to 'Baba is You.' With a little more convenient controls, I would definitely play this as a full game!
Also, the music is great in all levels, but the level 13 song is phenomenal