I'm a big BB King and the first two times I saw him, he was really great, even at this advanced age. The final time, though, the Thrill Was Most Definitely Gone. He played snippets of his own song, interspersed with about a dozen renditions of "You Are My Sunshine," while flirting semi-coherently and quite embarrassingly with a woman in the audience. It was clear his band was milking him for a few more paydays before he checked out completely.
About as bad was an outdoor Chris Isaak show at local winery, which was interrupted by a lightning storm. Venue operators completely unprepared and about 2,000 people crammed into space designed for about 200 (others went to cars, busses, etc.). They tried to address an increasingly unruly crowd but no one new how to use the internal PA system. Tried to use a bullhorn but instead triggered a loud police siren. Once in the room, they wouldn't let people leave, because walking to the cars would be unsafe. When they finally admitted that the should won't not, in fact, go on, they tried to keep people from retrieving their belongings (which we'd been instructed to leave behind in the rain) from the concert area -- that didn't last long. In short, we saw about five songs during a frustrating 3+ hours, got soaked, and generally had a miserable night.