Yes, Giorgio was one of the biggest mistakes Pavarotti ever made. His
singing was very good (would have been significantly better had the
film been made just three years previously though), but as you said,
poor English and Pavarotti was really uncomfortable in his role. He
also put on a huge amount of weight (when he tried losing it
specifically for the film) and was uncomfortable with many things that
he was required to do, the result was embarassing. This disaster of a
film probably prompted the infamous booing during the Serra/Pavarotti
Lucia di lammermoor performances at La Scala in 1983.
In terms of acting, Pavarotti was no Mario Lanza. And I'm very glad
that Pavarotti never did make another film.