The lack of variety...
There's only one thing that I thought brought this piece down from being truly great... the lack of variety in the instruments.
Imagine, say at around :52, some background violins could come in, or maybe some other instruments -- the piano would be a magnificent opening, and it would be an amazing piece.
I kept on expecting an amazing entrance, a whole orchestra of instruments... but I felt a bit disappointed... it's just such a beautiful piano piece -- with anything backing it up, it'd be so amazing.
Still, as a piano player here, I loved it anyways. The chords sounded great, and the music sounded crisp (If it turns out this isn't a piano, I'll feel stupid. :D). The tune's catchy, and it's something that I'll probably remember a day or two from here.
The lack of variety and a rather repetitiveness to the song bring it down -- it's so close though!