So Cinny, do you consider these a single album or a double?

What about acts who released 2 separate albums at the same time (Bruce Springsteen, Nelly, Guns N Roses), a deluxe version, or different versions of an album (like a Target/Barnes & Noble exclusive or one for Japan)?

Double-albums are tricky. They should be a little messy and with some unusual stuff, but not too messy or unusual or it feels like padding. Another thing is that some 60/70s'-era double-albums can fit (or nearly fit) on a single-CD nowadays, so are these still considered double-albums?

I love Blonde on Blonde, but two or three tracks ('Temporary Like Achilles' and 'Obviously 5 Believers', and maybe 'Absolutely Sweet Marie') strike me a filler to pad the recording up to double-disc length. The recording sessions suggest that Dylan wasn't even thinking of a double when he started recording it, but maybe after 'Sad-Eyed Lady of the Lowlands' went on for 11 minutes, he started to think it could be.

The White Album (actual title: The Beatles) is still the best, maybe. 'Revolution 9' (which goes on for 8 minutes) isn't so much filler as it's just an arty recording that would never have passed the quality-control test of a single-disc, but was allowed to go out on a double. (John's 'What's the New Mary Jane', which is also pretty dire, was only pulled from the track-list at the last minute.)

George's All Things Must Pass was actually a triple-album on vinyl, but the last disc is just filler (not very interesting jams). The first two discs are great, though -- despite Phil Spector's over-production -- and certainly rank it high among double-sets.

Exile on Main Street is really good, though I think a few songs are below par (as with Blonde on Blonde).

A less famous one I really like is Joan Baez's Blessed Are... (1971). Recorded in Nashville and her last LP on Vanguard, it's a really interesting listen that has some good original songs written by Joan (which is generally rare on her LPs) and the usual tasteful batch of cover songs, including the big single "The Night They Drove Old Dixie Down". Very rich album.

Songs in the Key of Life is likely the most impressive of all in terms of one person doing nearly everything. Well, Stevie had some great brass musicians and Sembello on it, but still he did the lion's share, which is insane given how many amazing musical ideas come roaring out of it. It's just a staggering work of genius.

Sign O' The Times is one that probably doesn't really need to be a double album, given that there are 17 tracks (it actually just fits on one CD, doesn't it?). But anyway, it's incredible (well, here I am on a Prince site, so...!).

Those are the ones I thought of off the top of my head...

[Edited 6/2/18 6:48am]

[Edited 6/2/18 6:48am]