His other spy dramas, like NORTH BY NORTHWEST, may be more fun, but none of them are as realistic. In fact, very few spy films have the authenticity as TOPAZ. The story is based on fact. In 1962, a Russian top-level KGB defector informed the U.S. that some very high-level French diplomats, in a group called "Sapphire", were selling secrets to the Soviet Union. TIME Magazine printed this story in April 26, 1968, and did so using the same source that Leon Uris did: the U.S. sympathizing (and exiled) former Chief of French Intelligence, Philippe Thyraud de Vosjoli.
Incidentally, a viewer needs to know the chronology and key events surrounding the 1962 Cuban Missile Crises as background, or else the film will be confusing. I suspect many critics condemn it because it's easier for them to dismiss the film rather than confront their own ignorance.
Not that this movie is without weaknesses. Hitchcock was no realist, and the grim world of films like THE SPY WHO CAME IN FROM THE COLD is probably the type of ambiance it should have presented, but doesn't. However, I definitely join the camp of those who consider it underrated. I read writers on Hitchcock who unthinkingly rank TOPAZ with his worst stuff, and yet many of us prefer it over THE TROUBLE WITH HARRY, MR. AND MRS. SMITH, and other Hitchcock works that don't get castigated as nearly as much. I can't help but suspect they receive less criticism because they are more typical Hitchcock. This film is atypical Hitchcock, so readjust your expectations accordingly.