Simple but competent pixel art.
The same cannot be said about gameplay: the game's physics is badly adjusted. I really like challenging platforms, but yours take away the players's freedom when prevents controlling speed when we jump. This makes the character movements uncomfortable and spoils the player's fun. There are smarter ways to make a difficult but fun game.
In addiction, some sections prevents our progress with some weird "invisible walls" and the player's speed need some polish.
An positive point was the wall jump: remember me "Super Metroid" on snes, which is hard but pleasant to master.