Thank you, if there is sufficient demand I would be happy to include more levels or even make a sequel with larger levels. The difficulty curve at the moment is really all over the place and could definitely use more levels.
Yeah, maybe a number of stage "packs" or "worlds" (maybe "floors"?) or something that each introduce a new mechanic in a tutorial level or two, then include a handful of stages that are harder and incorporate mechanics from previous floors? Just an idea. :)
Great job including opening & ending cutscenes, by the way. Those make it feel much more complete as a game, and a lot more satisfying to finish! I can tell you spent a lot of time considering the player's overall experience.
Actually the level scheme that you described is what I have (more or less), there are simply too few of levels overall. As a game jam, I wanted to keep the game short, so that more people could actually finish it (we all know that people rarely spend too much time playing each jam game).
My goal with the game length was to have enough levels to allow a player taste all abilities and mechanics, but to leave them wanting more :-)