Book and Movie
The book is obviously written by a dedicated classicist. You either into that sort of thing or you are not. If you are, as Roger De Bris would say, "It's full of historical goodies." Otherwise it can be dense and pedantic, not unlike Lew Wallace's BEN HUR. There have been more recent translations which may be more readable. I haven't read them but perhaps one of the other posters can comment. The best and most readable book of this genre is/are Robert Graves' I, CLAUDIUS and CLAUDIUS THE GOD.
I've often wondered why Henryk Sienkiewicz --- or his estate --- didn't sue the writers of THE SIGN OF THE CROSS for copyright infringement. Except for the ending, they're virtually the same story.
As for the 1951 movie, I thought Robert Taylor was too old for the part. Ditto Deborah Kerr, but she comes off better than he does.
Of course the best roles are left for the character actors. One of my favorites is Roslie Crutchley. She was also good as Madame DeFarge in A TALE OF TWO CITIES, the housekeeper in THE HAUNTING and a nun in THE NUN'S STORY.