The conventional wisdom is indeed largely correct; this movie is a disgrace to a fine play. Even allowing for the complete lack of singing ability of the leads, what should be the best parts of the performance, two magnificent songs, are handled disgracefully. Compared to the play and the original cast album, the film was such a shock that I've avoided it for decades, and was tempted to desecrate the grave of whatever Hollywood executive decided to remove Richard Kiley as lead.
This was somewhat unfair; I'd forgotten how well-handled the lesser parts of the movie were. The minor roles are very well done, both in acting and (mostly) in singing, and Peter O'Toole can indeed act when he's not pretending to sing. His vigil, and his penultimate scene, for instance, are very moving. So if you make a determined effort to forget Kiley and Diener temporarily, it's worth renting occasionally.
This was somewhat unfair; I'd forgotten how well-handled the lesser parts of the movie were. The minor roles are very well done, both in acting and (mostly) in singing, and Peter O'Toole can indeed act when he's not pretending to sing. His vigil, and his penultimate scene, for instance, are very moving. So if you make a determined effort to forget Kiley and Diener temporarily, it's worth renting occasionally.