Great little puzzle game! I loved the look and feel, and the mechanics were introduced well and gradually. Very interesting that something which might seem like a glitch was taken to be an important mechanic! Probably my favorite I've played so far.
Unfortunately, however, I couldn't get past level 14, which it seems is something others encountered as well. It was mentioned about "controls" and "skill", but I think the main issue here is that there are primarily skill-based levels in what at first appears to be a puzzle game. The controls are fine for the puzzling, and people who make to the higher levels are likely quite skilled at solving puzzles, just not so much at tricky button combos with precise timing.
I think it would work very well if you cut the parts that are dependent on quick, repetitive, intricate, and/or precisely timed button presses. These include level 9, 12, and 14 (and possibly others later on). For level 14, I think it would work if you just moved the heart to the center horizontally, while keeping it where it is vertically. For level 9, if you just cut the need to hit "D" again after jumping and pressing "A", it would be much easier but still retain the same spirit. For level 12, it would help if you moved the heart a bit closer or further down (while still requiring use of the pushing), or even had another platform grow out of the bottom-right corner to catch you as you fall that would be good.
I remember Mark actually mentioning that he had the same problem with Mind Over Magnet, so ended up cutting the skill-based parts.
Other than that, though, I really liked it :)