Although I would never want to read the book because, quite simply, the main characters, the Trevelyans, are both kind of idiotic. The first paragraph of the wikipedia article is quite accurate:
He Knew He Was Right is a 1869 novel written by Anthony Trollope which describes the failure of a marriage caused by the unreasonable jealousy of a husband exacerbated by the stubbornness of a willful wife. As is common with Trollope's works, there are also several substantial subplots. Trollope considered this work to be a failure; he viewed the main character as unsympathetic, and the secondary characters and plots much more lively and interesting. It was adapted in 2004 by Andrew Davies as He Knew He Was Right.
Mr. Trollope was right: the secondary characters are fabulous and extremely entertaining. Here is a run-down of my favorites, some of them played by actors whom I recognize:
1. Bill Nighy plays the trouble mongering Colonel Osborne whose visits to Mrs. Trevelyan cause all the trouble in the first place. Bill Nighy is perfect in a role where his motivations can never really be known since his words and reputation conflict with each other. When he turns to the camera to justify his actions, it's a pleasure and absolutely hilarious.
2. The romance between Nora Rowly and Hugh Stanbury is adorable. Nora is the sister to the Mrs. Trevelyan, but remains gorgeous and calm through the whole ordeal. Probably because Hugh is so awesome and clear-minded as well. They fail to see that the other person is as into them as they are, but that resolves itself quickly enough. One of my favorite moments is when Hugh is trying to flirt with Nora, and Nora won't have any of it, and he starts his own sililoquy with "Damn, damn, damn, damn, damn." Said by a man with a cane is quite endearing.
3. Mr. Glascock is Nora's spurned lover. Well, he politely proposes, is politely refused, and goes on living a rather polite life. He sports a fantastic mustache, and eventually falls in love with an American girl with an implacable accent (is she supposed to be from the South or Midwest, I can't tell). Mostly, any character with any degree of common senese is preferable to the main characters and are automatically a favorite.
4. Mr. Gibson, played by David Tennant, is a town vicar who is initially taken by Dorothy Stanbury, but is rejected. In order for his reputation to be saved, a Mrs. French forces him into an engagemnet to one of the Misses French who he has flirted with for seven years, and both of whom are in love with him. Hilarity between awkward characters ensues, including one of my favorite turn-to-the-camera moments.
5. Jemima Stanbury is the spinster aunt of Hugh and Dorothy, and, much like Diana's spinster aunt in Anne of Green Gables, she is rich and convinced any one who comes near her only loves her for her money. However, she grows fond of the very good and very kind Dorothy, and enjoys the pleasant Brooke Burgess. Adorable.
6. Last are my two favorites, Dorothy Stanbury and Brooke Burgess. They have to be the most amiable characters ever written. Brooke is played by the charismatic Matthew Goode (who I fell in love with here, and am shocked when he's awful). Anyway, Dorothy and Brooke fall in love very quickly and sweetly with plenty of good humor.
In fact, all you really need to see of this miniseries is the following, which only features scenes in which Matthew Goode shows up. It misses some of the pseudo-obstacles for Brooke and Dorothy's relationship (letters written, objections given), but that was all ridiculous anyway: