Even only the Firth of Fifth's particular approach to repetition with different instrumentation (the piano intro cascades later on with synth, the flute and the guitar solo), cheap as it is, but combined with the breathtaking melancholy of Hackett's work in particular would make me vote for it against a lot of tracks. I have moved on to other Gabriel-era albums since (and even on this album, I tend to prefer the Cinema Show nowadays), but this used to be one of my favourite records and I still hold it in very high regard.
And mind you, I really like Atlantean Kodex and The White Goddess is probably their most consistently enjoyable album for me, but this time it's personal, so my vote went to Genesis immediately.