Thank you for your feeback!
You can make small jump and big jump while walking or running, but being able to modulate the height depending of the time you pressed the jump key would be way better, I'll had that in the todo list!
Removing the running key, and fix the moving speed at the current running speed is something I added in the possible gameplay modifications.
I planned to create the levels again, possibly from scratch. That's probably the main issue of the game right now!