This was a really great little experience - the platforming felt really nice. The controls were really smooth and allowed you to provide a few challenges that required tricky manoeuvres that didn't feel frustrating or unfair. It played like a professional platform game and the puzzles were well constructed. The art work was fantastic too - I thought the ghost phasing power looked and felt really nice to use.
Your choice of music and sfx were enjoyable too. It felt quite calming and contrasted quite well with some of the difficulty of the later levels. I got a Final Fantasy / Breath of Fire vibe from the soundtrack.
You should expand this into a longer game with a narrative - it's got some real potential!