Can an author rate a film of his book?

Q: How can an author rate a film of his book?
My employer, mentor and friend, Robert H. Adleman answered that question soon after the release of the 1968 movie, The Devil’s Brigade starring William Holden based on his nonfiction book of the same name.
A: He can’t!
Bob explained in a newspaper article:
I hear that “The Devil’s Brigade” is one of the most exciting war pictures to come along in quite a while. And everyone who knows that I wrote the book on which it is based has asked me if I’ve
seen it and how do I like it.
I tell them I think it’s great. What am I going to say?
If I tell them that for two hours my wife and I sat in a private screening room and alternately squirmed and held our breath as the scenes we knew so very well flashed by, but at the end of it we couldn’t say whether it was better than the latest Oscar winner or as interminable as an Andy Warhol movie, they would put us down as a brace of filberts.
It’s the truth. I really don’t know how to grade it.
---Robert H. Adleman
Philadelphia Sunday BulletinMay 12, 1968

Privately, like any author, he was more than pleased that his first book had made it to film. He felt like he’d hit a grand slam: Hardback, movie, and paperback. He stated that each creative effort should stand on its own merits and he could not offer an objective opinion.

On a personal note, I loved the author, the book and the movie. Of course, I am as biased as any family member or friend might be. The book was co-written with Col. George Walton who, as an attachment, was a member of the World War II unit referred to as the Devil’s Brigade. Walton did most of the required interviews and research. Adleman took four months to bang out the manuscript with his two-fingered typing technique.