Cute player character. Not much to comment on since it's clearly in very very early dev but there are a lot of directions you could take this. It feels like there's a bit of acceleration to the player movement, not much, but if it was a little heavier (like in the first mario) you could do some interesting things between that and the analog jump. I would recommend finding a tileset that doesn't have holes in it as well lol

Congrats on making your first game! 

The very first thing I would add is a way to restart quickly after dying. The pixel art looks really nice! Since this is your first game, try to make your first levels really simple. Keep at it, you'll get better over time!

Its defenetly a great starter.
I would suggest you learn to how create a start menu to learn how to handle scenes better.
Then you can add win/lose/pause etc.

Also, note (for the future) that collision box (with walls/ground) is usually pixel-precise so thew character doesnt float, while the hitbox (hurtbox) is usually smaller than the player sprite itself.