The difference between Yes as an instrumental band and most other bands was that they in their classic line ups (including both Bill Bruford and/or Alan White on drums), had chemistry. They were the prog equivalent of deep purple's HM classic line up; you can hear the musicians feeding off one another throwing out licks and riffs - creating more than the sum of the parts.
But the biggest difference between Yes and any other artist is Jon Anderson's songwriting; he does not write conventional lyrics at all - he transports you to another world, really takes you out of yourself into a world of pure emotion with only a few physical objects to focus on,and he's obsessed with music, but there are love lyrics, spiritual messages and blues themes (for want of a better term). As Rick Wakeman always said prog rock has got to be the Blues - if it's not then it's rubbish.
"Close" is a rich powerful symphony of a rock album, and everyone's got to get a listen to it or lose a valuable experience.
Recommended parallels: Hendrix Electric Ladyland, Moody Blues In Search of a Lost Chord, the Who's Tommy and Sell Out, Yes' Tales from Topographic Oceans and Relayer.