Wonderful dualism
Briefly: fantastic composition.
In depth: The very beginning actually reminded me of Thomas Newman's soundtrack music (e.g. the more upbeat lines from 'American Beauty' and 'Shawshank Redemption'), specifically because you chose a soft piano. The next line with the synth strings and the harder piano take it up a notch, destroying the Thomas Newman image of flawed, stagnant beauty. Then the club percussion kicks in, feeling dark, heroic, and forceful. But behind the club is the original theme, sometimes with the original piano. It's as if sadness is somehow providing motivation for action and motion. The image in my head, oddly, is of a grown-up Haley Joel Osmond suddenly thrust into the world of the Matrix and trying to make his way among the chaos. The remainder of the song was thoughtful, but driven, always referencing that original feel but covering it with a dancing, animalistic rhythm. It shifts between two ideas: the thoughtful confusion of the piano and the determined certainty of the club sound, and it ends with a quiet mix of both transitioning to an ambiguous and toneless noise that merely fades instead of a final conclusion on either sadness or certainty. This above all leaves the entire song open-ended.
The progression of the whole song is a wonderful story-like arc without having a story, full of promise and imagination and open to infinite interpretations. That's why I think it appeals to so many people!