Well...I only saw the Nine Tailors (sorry if I wasn't clear...the only one I've seen OR read) and I thought it good both printed and filmed. I'm intrigued by the English change-ringing of churchbells. I thought it took at least two entirely unpredictable twists which left his Lordship as baffled as the reader, bringing the reader along on the voyage of discovery...which to me, makes the story superior to the Poirot stories, where the hero always seems to know certain facts not revealed to the reader, or other characters, until the last minute.
The one criticism I've heard of teh BBC production is that Lord Peter didn't look like he's described to be in the book. I never saw the TV series, so I'm not sure exactly HOW he was different.
He's not supposed to be a very attractive guy, and maybe that's what they changed? His charm is in his wit and personality, not his appearance.
I remember also being really disappointed when I saw the BBCs Tommy and Tuppence (Agatha Christie detectives) shows. Tommy was supposed to be a short little red-headed guy with kind of a pug nose and likewise not that great looking. Instead, they have him played by a tall well-dressed guy with dark hair. Bah!