Double albums are interesting because many times they represent a emesis of ideas during a particularly fruitful ideas of a group or artist.
I did not list two of my most listened-to double albums - The Beatles and Tusk - because though I feel they are tremendous albums, they are FAR from cohesive, tight albums...I guess out of my list, Electric Ladyland fits the bill too. So many ideas are jammed in there, such a variety of styles juxtaposed together, one can see why they might be polarizing. I find enjoyment and greatness in these three (and with The Clash's London Calling (and to a lesser extent Sandinista) because of the randomness, the excesses, the wild shifts in tones.
Because this seems to apply to most double albums, there may not be a "perfect" double album in the sense one might judge a tight single album where singular tone, themes or moods often are the focus of at least many a critic's interpretation.