This is a really great first game project! Most interactions have a sound paired with them which is so important, and you've got some jump input buffering already for a nice responsive jump.
Two suggestions for you: You've already got jump buffering, you should look into adding some coyote time to go with it for a great feeling platformer. For a small moment after walking off a ledge let the player still jump. At least two of my deaths in the game I think would have been prevented by coyote time, right now if you're just a tad late on the jump you die. In addition to this, I would look into adding some checkpoints in the game to respawn at after the player dies. It's really rough having to start all the way back at the beginning.
Awesome job!