My first gigs were mid 70's (Slade, Alice, Who, SAHB, Little Feat) then it sort of exploded into too many to mention but there was only one gig that stands out head and shoulders in the disappointment stakes and that was a Tonka era UFO and a drunk Mogg - such a shame - Zep at Knebworth was shaky but still enjoyed it (excluding a broken nose from a beer can hailstorm) - Page's overproduction is not replicable on a stage...
otoh Rush, from 1st UK tour in 77 to last time I saw them in 07 were perfection, every time, and Allman Brothers Band and spin-offs (DB Gt Southern, Sea Level) were outstanding, and...
Turkeys...? well Sabb's with Gillan and Gregg/Cher were dodgy, but watchable, in a perverse sort of way... at least with the Sabb's gig I got to spend some time backstage with SRV and co which with their set was the high point of the day; that and the roadie's bar...