Poor, yet not as bad as Caine says I saw this recently with my wife and discovered it's better than Caine believes, although it's not much cop. Britain's greatest ever screen actor does not seem too interested in this role, which is a pity as he might have elevated it with more conviction in his playing. Rex Harrison seems even less bothered, perhaps unsurprisingly, as his character is very poorly written. William Holden is better, but his screen time is fleeting and, again, his character is not well scripted.
Beverly Johnson is as beautiful a woman as I have ever seen, but is given very little to do, the film might have gained a great deal by concentrating more on her story. Ustinov steals the show, but basically by playing a comic character quite out of keeping with the film's serious tone. The music is poor and Omar Sharif makes one of his many pointless cameos (his career has been based on this for decades now).
Richard Fleischer has to be blamed for not directing this more effectively, he was an infuriatingly unpredictable film director, and this is one of his weaker movies.