Like a slug, but lava. Great game! It feels clean and polished, it feels good to play, the tutorial was clear and levels were well tuned difficulty for a short and sweet experience, and it reminds me of pathfinding algorithms (a bonus) and the classic mobile Flow Free game were you draw lines between points on a grid and they interrupt each other. My first thought was 'Oh no it's the freaking line crossing phone game ahhh'. I could easily see it getting more complicated too. I saw in another comment you scoped it down, I'd say that was a good choice. Something like side objectives would be a good contender for a reward for skilled players.
Constructive criticism: Feels like a mobile game (probably because I was thinking about the mobile game and the simple design of it). It didn't feel like I was forced to learn anything with how I could mostly complete the levels in one try, reminds me of the GMTK puzzle design video (roll credits) where you misdirect first and therefore learn and analyze the structure that gets in the way. Also, I wish completing the level was more satisfying as it's just a quick cut. Maybe animating the entire room being filled will lava would be satisfying
Yeah going to echo others and mention small tweaks. I wish the green/red blocks were clearly split, sometimes I wasn't sure if it was 4 or 5 total so it made me second guess myself. An undo button with limited uses would be nice (command pattern lets goooo).