Yes, Robert Harris is patchy but there are some gems in his back catalogue. There’s a whole trilogy about Cicero (Lustrum, Imperium and Dictator) which are all great. An Officer And A Spy is good too, about the Dreyfus Affair.
My other recommendations would be The Garden of Evening Mists by Tan Twan Eng and The Narrow Road to the Deep North by Richard Flanagan - both fantastic books springing from the Far Eastern theatres of WWII.