Good, easy to grasp.
Unlike "Portal" based games this relies solely on platforming and folding the level. While understanding the way that things fold into each other, or are necessary to unfold, does require some creativity, the simple controls mean that the mechanics never get in the way of the puzzles, which is good for when you'd like people who don't often play puzzle games to try it out. The music loop is nicely atmospheric without being obtrusive to the experience and the character sprite stands out well against the background.
While puzzle games typically require a specific solution I think that the use of the fault lines here could open up the possibility of having stages that have multiple potential solution paths. The level design would need to be even more tightly done, but I think that the the game creator would be capable of that.
To the person who complained about the jumping because of ceiling spikes, the only level where that seemed like it could have been an issue was way back on Room 6 and really the trick there is that you can simply be patient and walk onto the platforms needed without any risk of hitting the ceilings.