Oh man. Alright, I beat the game in one sitting. That was pretty brutal, by the end there. Two of the 900 levels (903 and I think 901) made me notice the unforgiving nature of the jump timing - either there's a frame delay on the jump or it's not picking up interframe input until the next frame, which would not be an issue unless framerate is locked at 30 or 60 fps or something. Fraps won't give me a framerate count so I'm not sure.
907 was basically impossible until I switched to controller; my fingers can't do all of that at once, apparently, but toggling on a stick in short-time-frame sync with a jump is apparently much easier. 910 was brutal. It was difficult to execute, yes, but I figured out the correct motion pretty quickly, and had to spend the next fifty lives guess-and-checking every possible jump-off-point and midair jump timing until I found the correct one. then dying at least three times to the sawblade on top of the left-side pillar didn't help the situation.
I definitely like the game, though. The auto-walljumping was novel, though a little strange, and definitely killed me a couple of times sliding down vertical shafts - trying to move away from the wall resulted in a suicide jump into a pipe. the walljump-direction limiting was a little strange; I get it, you need to prevent climbing, but there were a few levels where I would want to walljump around a hazard and then land on the inner wall of the next platform over, which I could not because walljumping simply didn't work. If this was somehow explained graphically (character leaps and points in a direction and doesn't turn back around even when he is falling back in the other direction), that could help, but otherwise I think I would recommend allowing for walljumps on different walls pointing the same direction, or design levels such that it is not tempting to try.
Side note: it might be nice to get some indicator of whether double-jump is still available, e.g. Mute Crimson + sparkles or Tinertia's backpack glow? Also, the death-respawn time is frustratingly long. (yes, two seconds is frustratingly long. The quickest comparison is Super Meat Boy, which puts you back in the game in a fraction of a second, and is awesome, and despite being ultrahard, is not frustrating). If the death animations are important, maybe don't also make us wait for the screen-cover fade?
Anyways, cool stuff! I'll definitely be back for the last ten levels when the full version is out. Good luck!