Hello! Many thanks for the very encouraging words. It makes me happy when some design intentions get through, the idea behind the early rooms was to provide blocking obstacles that could only be overcome with the new tools (room 1 - learn about fall damage, room 2 - breaking platforms, room 3 wall sliding, room 5 - combine wall sliding with breaking platforms to prevent fall damage --- so on and so forth). This probably didn't mesh too well with wanting to create e bite-sized metroidvania. Although there is a little bit of backtracking, the small size of the world makes it feel pretty much linear.
Totally agree with the need for an extra checkpoint in the wall slide room, splitting the challenge in half. It was a bit rushed.
Cheers