In no particular order:

Eric Clapton - excellent player but zero personality live. Could have stayed home and put on one of his records instead.

Queen - Not surprising given the vocal complexities of their songs. Freddie in particular struggled to reach many of the notes and Brian May's playing wasn't that inspiring.

Black Sabbath - First time they were great, second time they had major technical problems with the sound which could not be rectified on the night.

Gary Moore at St David's Hall - the balance of the sound was all wrong. The bass was far too loud, which meant that all GM's solo's were drowned out. Me and a mate even went to a different part of the auditorium to see if the sound was better. It wasn't.

Rainbow - Yet again Mr Blackmore was a great letdown live. Played for himself not his audience.