Yeah, with this type of platforming where you are required to make precise jumps it can be more challenging when the character needs to build up their velocity. It isn't always a bad thing though if it's intended to be that way, there are plenty of platformers that are similar, if not more extreme than yours.
The jumping did feel a little off though, maybe that mattered more than the character's speed. With a variable jump height like you have, I prefer to be able to make super tiny "hops" when i just quickly tap the key. Instead, your character jumps about 1.5 - 2 tiles high with a short tap of the key.
This is all just my opinions of course! You still did really well! I hope this helps and doesn't just come across as me being really nitpicky about it haha.
Edit: Of course I say that about your jumping, and then go back and play some of my own older platformers that have the same problem... ahahaha!