The game is a bit on the difficult side but also movement feels slow. You could make jumping more responsive by for example making the fall faster. Just search on YouTube "How to make any platformer better?" or "super mario jump" engine of choice.
Also, for me, it was weird that you need to press Shift, then A or D to dash, I'd expect that you can do the reverse as well, like if I'm holding A or D, pressing Shift should also cause dash, but it doesn't.