"It was bad. Out of 10, I probably would have given him a four. The music was all right but his singing was absolutely shocking."
Dozens of concert-goers streamed out demanding a refund resulting in what Mr Barton said was "a bit of a hassle" in the foyer.
Another concert-goer Shayne Thompson said the Glen Campbell experience was "the worst concert experience ever".
"The concert should not have gone ahead. Not only could Glen not sing, the band and the rest of the family did not know what the heck was going on with the rest of the show."
Mr Thompson said the promoters should have known he was ill and cancelled the concert.
Herald calls to Ticketmasters and a spokeswoman for Andrew McManus Events, the promoter for the concert, went unanswered yesterday.
His Wellington concert, which was to be held at the Michael Fowler Centre last night, was cancelled because of the singer's illness.
A Ticketek spokesman said all tickets sold to last night's show would be refunded but it remains unclear whether the Rotorua concert-goers would get their money back.
Before Glen Campbell left New Zealand for Brisbane, One News asked him whether it was likely people would get refunds.
"It is a good question," he said. "I don't know 'cause my daughters performed, everybody else did and I did too. [Although] I didn't sing."