Missed the Mark
Anna Chancellor is certainly capable of playing Lucia as written, but for whatever reason Lucia here is treated as a reasonable woman that Mapp often tries and fails to beat at her own game. In the books, Mapp and Lucia are quite similar in their pettiness and scheming, and I think that approach accounts for much of the appeal of the books. It's just missing here.
I didn't mind the shuffling of plot elements and even locales and the order of events into what they arrived at here, but it's the characterization that unfortunately just misses the whole appeal of the books.
That's probably the director's doing rather than Anna Chancellor's, but it's regrettable, as I think otherwise the series was great fun and I would have liked to see more done in time.