This is a framework of something really neat.
The idea of switching between arrow keys is pretty cool and it's something I haven't seen done before.
The music does not match well with the gameplay. It's slow and doesn't really have any notes that would immediately jump at you. The arrows are similarly sluggish. Even the hard difficulty, although it has the most happening in it, is still painfully slow.
Still, for 48 hours of work it's alright. With some serious work put into it you could make something downright groundbreaking.
Also, the ghost looks super cute. Animating him/her and putting them on the side could make for a neat feedback on how well the player is doing.