Nice simple game, good as you are learning new things.

In addition to what the other have already said, I would avoid to leave so many hearths around. The game is already very easy, so I would leave maximum 2 of them.

In addition I wouldn't destroy the heart when touching it if the princess is in full heart, this because a player might leave it for later.

Good as starting point of game, you can definitely build up more from here :)

A little simple, but pretty good for someone who's just learning! In the future, try mixing things up more-- like new types of enemies, or making the game look different over time, so the player is always discovering new stuff. Also, I didn't know there was an attack until I saw the other comments; the first time I played, I just ran past all the skeletons since I didn't realize I had a sword.  Always make sure to tell the player what tools they've got in their arsenal!

I wish I have some sound feedbacks while hitting the enemy.

Nice effort, like the pixel art style and the minimal skeletons. One bit of feedback would be to add some audio for getting hit and for sword swipes it adds feedback to the game mechanics and makes it more fun. 

I love this type of theme and how challenging it is although I would make the skeletons hitbox a little shorter, overall I like this a lot! 1 question tho, I am wondering how does this relate to the theme?