That was a generous demo and a lot of fun. I finished it on Steam and started the B-sides (I only beat the first one, but that was for lack of time to keep playing). My advice to players: if the upgrade seems very far off, then explore. My only bit of feedback to the dev is that I would suggest making it *very* clear to a new player that there is somewhere new for them to go to after they get the wall jump upgrade. Maybe a camera shift/pan that happens whenever they are standing near the first level's start (unless they have since visited the second level), but I think something to make the availability of a new area clearer would add that extra bit of polish to the game.
And having finished the B-sides, yeah, very cool, lots of fun, and I can't help but wonder if the new wall material is a hint of what's to come. Also you might want to know that in the current Steam version you have what I interpret as being a bad respawn point in 3-B right before the short zig-zag fall near the top of that portion - it's the same respawn point as in 3-A but the B-side has no floor there.