That's a definitely a wonderful entry. I had a lot of fun with this really creative and engaging gameplay! Lemme try to be helpful somehow.
Theme:
Hmm actually it might be the part that I had most problems with. It might be just me, but I really struggled with noticing the theme in the game (I mean that no matter how I've played I felt that not much is influenced by the way I play). Sorry if it's because of me being blind >_<
Visuals:
Oh you did an amazing job out there! It might feel very simple, but you made that simplicity truly elegant. You've chosen great color pallete making everything clear and well fitting, made that little effect of squares floating up and down in a pretty way adding a lot of life to the environment.
You've made a nice transition between levels and your UI is beautifully done (love those little info boxes, you even put ideal amount of information out there) Great job on that!
Actually there's not much I can recommend here, maybe you can try to play a bit with postprocesses (be careful as they are pretty rough on webGL builds), like adding things like: chromatic abberation, little bloom, vignete or grain. Just some loose idea, you can tweek with the values to try something that would really fit your game.
Another thing might be adding some life to some things like enemy spawn, or death. You can try creating some particles that might fit into the style.
Innovation:
Oh your game is great in that scope too. Never seen something like that before. Easy concept but makes for a really good game. You can easily try to add some additional content like maybe some: portals, keys etc to make place for more variety of maps.
SFX:
Sounds were pretty good, but you can try to randomize pitch by just a little every time you play the sound, so that it doesn't get too repetitive over time. I really missed some relaxing, calm music in a background, it would feel really good. Music is really important part of the game, so it's good to not forget about it.
Gameplay:
As I've mentioned earlier, gameplay is easy, but creative and requires a lot of thought at further levels.
Great job on that.
Game Design:
Game felt really good, from the very beginning to the very end (I really appreciate that heart at the end, it really satisfied me beating all the levels). Difficulty level progresses really well (maybe I would just add 1 level between 1st and 2nd with difficulty between them, as it takes a little time to fully understand mechanics of the game, but apart from that rest of the game was great.
Thank you for that lovely submission. That's another amazing game from that jam :)