I'm with Bosk, I think. LOVE the Big Medley on ACOS. I always liked the "The Lamb.../Musical Box" medley on Seconds Out. LOVE the "In The Cage" Medley on 3SL (perhaps my favorite recorded moment). I don't care for medleys that seem a sop to a certain fan base (both Rush and Genesis used to put medleys in that seemed only to serve as a "STFU" to a sector of a fanbase). I was NOT a fan of the Instrumedley, which seemingly had four bars here, three bars there, four bars back to song I, two bars tere, back to song one for a bar and a half, then three bars of song two, etc. Not true, I know, but it seemed it.
Put a different way: when used to throw a bone and cover an entire sector of the catalogue, no. When a very creative, new way of presenting a song or two, yes. When a creative way of having fun with a set of covers (like the old Genesis ending to "Turn It On Again", even if I didn't like the songs they chose), yes.
Best medley ever (by a long shot): Suite Charlotte Pike/Abbey Road medley.