Do you play pure platformers like Celeste or Meat Boy? The acceleration can't be low in those otherwise it feel unresponsive, it doesn't accelerate to max speed instantly but it's very fast. What exactly couldn't you figure out in the third level? Here's a solution: https://my.mixtape.moe/iaqcjn.mp4 What do you mean by wall jumps? If you couldn't pass the third level you haven't yet reached any levels which require wall jumps.
Viewing post in Citadel of Celestial Cascades demo (youmu-wip) comments
I think I grabbed a different version or something, those ghost enemies looked different in the demo I played and the third level didn't look like that, and I think the game page has been changed since I downloaded it. That said, no I haven't played Super Meat Boy or similar games before other than some other people's demos. Maybe if I'd played it with a controller the acceleration and direction changing wouldn't seem so jarring, but I didn't feel like it setting it up. The game is also quite a bit smoother in that video, so maybe my system had to do with it.