Melody is too strong.
You have a nice melody. It's basic, just a major arpeggio with the top note gradually getting lower, but it's still good. No, the main flaw in this piece is that there is nothing else. (The chimes in the background are so quiet they don't count.)
Well, no, I am mistaken. The main flaw is how unpolished this sounds. At the ending, you have a sliding glitch. That's kind of a "WTF" thing considering you're doing this on a computer. Ah, you're using GarageBand. Well, in that case, then why is everything offbeat? There's a little button that aligns everything to 1/4 notes, you know.
You might also want to make the theme bells or chimes. It would make it more spooky.