The A&E TV series, "A Nero Wolfe Mystery", rather faithfully adapted the books. There were a few minor changes. For example, the books were written from the 30s to the 70s, but the TV series decided to keep it simple and set it in the 50s (with the exception of a few that contained plots which linked them to WWII and another which was set in the 60s).
There is one big change that does stand out. In the episode, "Too Many Clients", a man's wife is openly cheating on him. Later, the man snaps and badly beats his wife. When Archie Goodwin, Nero Wolfe's assistant, discovers this, he checks in on the wife and threatens the husband. I was a bit shocked to read that Archie originally sent the husband champagne.
I suppose that, at the time the book was written, it was felt that the wife finally got what she deserved. Obviously, in this day and age, a hero can't be shown rewarding a man who beat his wife.
As for movies that improve upon a bad book, check out "The Howling". The movie has virtually nothing in common with the novel. Director Joe Dante once complained that the book was so bad, he didn't want even the few, minor things that did end up in the film.
The novel was more faithfully adapted as "Howling IV: The Original Nightmare". Watch them back-to-back and see why one is considered a werewolf classic and the other is basically forgotten.