2. Firth of Fifth
Wow, what an evocative guitar solo. Perhaps Hackett's finest moment with the band. Chills, man! The rest of the track is top notch, too. It all flows well and is like a nice gift to your ears. Love that piano intro. The synthy fanfare section before the guitar solo is also really nice. I suspect this song inspired Song for America by Kansas (I like namedropping Kansas all the time, since they're underrated and awesome). I'd also like to take this opportunity to say that Genesis has a lot of cool song titles.
1. Supper's Ready
What can be said. One of prog's premier epics. The heavy, apocalyptic subject matter gives this song a weight that separates it from the band's more oddball songs. Yet even this contains the highly bizarre Willow Farm, which is a nice change of pace from the rest of the track. Supper's Ready goes through many moods and styles and doesn't feature a large amount of repetition, but it still feels cohesive to me. The dynamic range is awesome, and demonstrates that prog drew from classical just as much as from rock.
One of the best parts of the song is the pretty, delicate flute melody after Willow Farm. And the intricate yet intense Apocalypse in 9/8 shows that the band could prog it up with the best of them. The epic's triumphant ending is absolutely amazing, and really set the standard for "How to Conclude a Prog Epic."
And that concludes the list. Thank you for reading.