This is a very well-composed piece, and I particularly liked the chord progression you used. I can see from your interesting commentary that you put a lot of thought into this aspect of the piece, and it paid off: the progression doesn't repeat to the point that it becomes predictable or boring (something that I have seen in a lot of Newgrounds artists) and it evokes a lot of different moods, sometimes stirring, sometimes more wistful. The voicings you used for some of the chords, especially at the beginning, were also quite interesting and helped keep my attention.
I liked that the piece had a clear structure to it. When working with a solo instrument, it's tricky to vary the tone of the piece to create a consistently engaging experience, but you managed to keep the piece engaging by starting out very understated and bringing the intensity up and down in a way that stood out.
Another aspect of the piece I thought worked well was the ambient noise supporting the piano at the beginning. Backing an acoustic instrument with a synth pad like that doesn't always work very well, but you kept it very tasteful by making it very faint, acting not as an outright harmonic support, but more of just an ambient drone.
In fact, one way in which I think you could have improved was by either continuing the drone, bringing it back later in the piece, or perhaps getting rid of it entirely--the thing is, it appears at the very beginning of the piece and then just disappears, which is kind of disorienting. Either removing the drone or making it more present would, I think, help the flow of the piece. (I'm a bit biased here, because I love minimalist music and drones, so I would just spread the synth over the whole thing--but that's just one way of doing it.)
The one other thing that I thought was a little bit inconsistent (and it's a very minor thing) was the presence of swung notes at 2:23 and 3:54. While I appreciated the rhythmic variation they brought to the piece, it was again a bit disorienting because no other rhythms of that type showed up. So, again, either adding in more swing or varying the rhythm in different ways would make the piece feel more consistent.
Really, though, I'm dwelling on small details here. Overall, the piece has a beautiful chord progression, contains an engaging set of variations on that progression, and combines a complex variety of moods. Great job!