Hey, I dug this a lot! Really fun Super Meat Boy-like. Some feedback, since it's still in beta.
-Having the wall jump be activated with just one key, rather than the usual two, feels really nice and makes a lot of sense! This was a super nice touch.
-Going through the exit door doesn't need to be a button press--if I get to the exit door, I'll obviously want to go through it!
-Respawn times could be much shorter. Steal the instant deaths and respawns from Meat Boy too. ;)
-I think there are a lot of tiiiiny tweaks you could make to the controls to make the game feel a little better too. For example, making it so that the upwards motion of a jump only lasts as long as the up arrow is pressed--this would change how the game is played a little bit and might require reworking some of the levels, like 503, but would make the moment-to-moment experience feel a little juicer. (Probably!) Maybe play with the acceleration a little bit too, during the split second between pressing the left or right arrow and reaching full speed?
-Some of the cooler particle effects feel a little out of place, haha. Like the cloud of blood that appears when you die--definitely rad as hell, but doesn't totally jive with the art style.
Really enjoyed my time with this though! Very fun platformer with some great level design. I like how the levels are sort of puzzle-y, and that you sort of need to figure out the right way to jump through them, rather than just executing a path you already know. Looking forward to playing the final version!