This is going to be one of the few songs I'm actually going to favourite. Not because it's perfect, but because the ideas are pure genius. The sounding of the piano could have been better. Personally I would have used stereo separation to open it up a bit, but basically my problem with is is that it sounds a bit too stale.
Other than that I think your song is amazing. You are one of the people I've seen on here, including myself, that are able to utilise tempo modulation in a good way :D.
The ending is a bit weak, and could have been better planned, but overall it's a great song that deserves 5 stars.