How do you describe Pink Floyd to someone who's never heard them?
 

Genre, overall sound, anything.

Retrospectively, I would say that Pink Floyd sound like post-rock if post-rock was made in the 70s. To me, they have very little to do with other prog rock bands, at least besides The Wall to an extent.

I would think if someone's never heard of Pink Floyd they've probably never heard of post-rock either.

Or language

I would describe them as a psychedelic prog band with massive popular appeal that went through four major stages: psychedelic pop, experimental psychedelic, conceptual prog, and finally a mostly bland final prog stage with a flare of their former brilliance popping up from time to time.

Why do you consider The Wall the most proggish?

Mostly boring.

The Wall is practically a prog opera, and features the greatest demonstration of their musicianship IMO. Their other work is less proggy in that it is repetitive and less virtuosic, and the others also don't contain as much of a story as The Wall.

The post-rock element comes out of the fact that songs like Shine On You Crazy Diamond or Echoes progress in a fashion similar to post-rock.

Do you consider Tommy and Quadrophenia to be more in the progrock realm than Dark Side and Wish You Were Here?

Hard to say. They're very different albums. I see what you're getting at with the Rock Opera thing. It's not the only factor tying in to my decision, but it is a major one. I'd say Tommy has enough prog elements to make it more proggy, but I'd put Quadrophenia about on par with DS and WYWH.

Hot garbage in a dumpster fire.

I'd say they sound a little like this