I recently finished a Great Courses about Roman emperors and the lecturer mentioned I Claudius multiple times as a good ‘novelization‘ of his subject. He‘s not wrong, but…
The novel can be dry and any dialogue is an info dump. Of course, Graves had no easy task and I can‘t see a better way to do it without losing integrity. And I suppose you could chalk the book‘s success up to Rome itself: it‘s telling how easily it takes you under its spell.