The art direction is amazing! Using the limited colour pallet was a smart decision for ensuring that art assets could be produced quickly, combined with good aesthetic style, and being able to produce so much shows that your artist is very skilled! (I think they also reused some of the leg walkcycles, that's really smart!)
The gameplay is very satisfying, I particularly enjoyed the spider mechanic. However, this is definitely minimal viable product, and it's clear where you cut corners to get it done within the timeframe of the game jam. This isn't a bad thing, just noticeable.
The QA could be better, there are a few bugs in the game like being able to move while refilling fireflys sometimes, and sometimes the physics glitch and you bounce around all over the place. Your music also doesn't loop forever. There is also the full screen issue (which is solvable, our team ran into the same issue during our first gamejam (I think we manually set the resolutions to some value, and make sure to use the minimal unity html5 template) My game's viewport is too big for the page, can i make it smaller with CSS? - Questions & Support - itch.io ).
Anyway, all of these are minor gripes. This game is really fun! Congrats!