The game is interesting. The mechanic is simple yet have something to thing about. You do not try to push it by introducing more mechanics or such, but rather keep it clean, and just let the player explore. This I like.
What I do not like is the level orders and the repetitions. There are multiple levels which are exactly the same, which I felt were quite pointless to redo. The level sequencing is also very weird since they are clearly not in increasing difficulty. Level 3 is the first level with some challenge, but then level 6 comes as a completely trivial level. Level 11 is, according to me, the hardest level in the game, but then there are a couple of more levels left, with the close to trivial level 14 in there.
I guess there is some easter egg going on, or such, with the order of the letters, but I didn't really bother to write it down and so didn't figure it out, so the only thing the ordering othe level did was lower my play experience.
So my critique would be that you should remove some repeat levels and do some reordering. Other than that the game is cool, fun, interesting and elegant. Good job.
... also on the technical side I really whish I had come up with doing this idea for a game with multiple player controlled characters.