Sorry about the keybinds - Z is a quite common jump button on keyboard for the games I play and I hadn't thought it was going to be an issue. I find it much more comfortable than any of the other options. The title screen does say to press Z, though maybe that wasn't enough?
I tried my hardest to make the movement satisfying, so glad to hear it felt alright.
The enemies were difficult to get working as-is, so we didn't go the extra mile to make them more interesting. Maybe a score counter could work.
As for the key change mechanic not being clear... yeah, we probably should've added an NPC to explain that. I guess we just hoped it would make sense to people once they hit the button, the music raised in pitch, and platforms floated up to form a bridge.