Yo! This is such a nice little package! You explained and executed the mechanics so well (in terms of introduction, mechanic evolution given the amount of time someone will probably be playing a Jam game, etc.) and wrapped it up so nicely. I hope to have something as solid as that next time I jam. For UX's sake, though, I'd take a look at the wall-snapping code when switching gravity. Sometimes, I'd see some odd jitter when veering too close to floating platforms and moving simultaneously while mid-gravity switch.  I'd also add an "ENTER to continue" on the level select screen, if you're looking for easy quality of life changes to make.

All in all, I really enjoyed your entry (even without the presence of SFX, but I'm with you... I never seem to have time for sounds, either)! I'd love to see where you take it, should you decide to continue with it. The feeling of catching yourself on a wall mid-gravity switch to avoid close-quarters projectiles is especially satisfying. Nicely done.