A few years after the LZ break-up, Robert Plant released a single called "Big Log". That is one of my favorite songs of alltime and probably the best best indication of what Zeppelin might have sounded like in the 80s had they continued as a band.
I don’t think I could pick a favorite Zep album. I just remember back in 1978 my friends and I were awaiting their next release for what seemed like a very long time. Presence had come out a couple of years before, but like you noted, it didn’t satisfy, and hey... we were nineteen or twenty years old and life seemed to move like molasses. We wanted and expected something like Zep I, or II, or III, or IV, or Houses of the Holy or Physical Graffiti. Something with hard driving Blues/Rock. Old school stuff, with an easy to play song or two for those of us who liked to fiddle with the guitar. (Ala Stairway or Going To California or Babe I’m Gonna Leave You)
But to us “In Through The Out Door” sounded like some sort of unholy cross between Elvis, The Beatles (back-beat stuff), The Beegees and Benny Hill’s theme song. It just wasn’t at all what we were expecting, and it drove us away from Zeppelin for years to come. Years later we joked that Zep had singlehandedly caused the birth of disco when that album hit the streets. :) (I actually ticked off a few people with that comment) LOL!