Beautiful artstyle! It would be nice if the main menu was a bit more interactive - for example, if elements reacted in some way when you hovered over them, Right now it feels a bit too flat!
Also! It would be great if the characters had interactions - maybe a short dialouge before each level? It would make this game more alive and more immersive.
Of course, I don't know what you're going for so these are just suggestions based on what i like in games!