I read the first 5 books in the Agatha Raisin series as a stress reliever during a busy summer. I liked them, but I didn’t love them. I read 6-10 (and actually I’m up to 12, now) out of ennui, because they’re always available from the library and they’re easy listening for my frequent long car trips. Six through 10 were not as enjoyable as the first five, unfortunately.
Books 6-10 see Agatha leave her small village in the Cotswolds 
and do some traveling (which makes sense; how many murders could possibly take place in a village before you start seriously considering the possibility of a Hellmouth?). Book 6 finds her vacationing in Cyprus, but 7-10 just take place in various other small towns around Britain. Besides solving crime, she’s dealing with a complicated relationship with her neighbor, James Lacey, as well as with her friend Sir Charles Fraith. It’s these two relationships that really brought this part of the series down for me.
Agatha has been in love with James Lacey since she first met him near the beginning of the series, but as time goes on we see that James is really not worthy of the love and attention she pays him. He’s cold, quick to anger, afraid of strong emotion, and has really terrible, outdated views on gender roles. Agatha occasionally rebounds back from him with Charles, but he’s awful in his own way: callous, selfish, and cheap. Watching Agatha flail through these relationships–desperate to make James love her, letting Charles talk down to her constantly–really cut down on any enjoyment I felt from the humor and quirkiness of these books. Agatha is a strong, well-rounded character, and she deserves better than these two bozos. I think Charles, at least, is supposed to be like a kind of lovable nitwit, but he’s just a putz. Charles and James are just not likable.
One strength of the books, however, particularly these five, is how well Agatha is written. As a mostly-single childless career woman in her mid-fifties, who is now retired, Agatha has a lot of time on her hands, and she feels it acutely. Her feelings of pointlessness and existential dread are surprisingly well-written, for a cozy mystery series, and make her an extremely sympathetic character. If there’s anything that keeps me reading these books, it’s Agatha.
As for the mysteries, they’re rote, but still interesting. There’s a fairly firm plotline: someone dies and is discovered, Agatha is somehow mixed up in the mystery, later on the book she and whomever she is hanging out with, either Charles or James, discover a second body and become murder suspects, eventually Agatha figures it all out with no help from the hapless police, the killer is caught, and peace rules again. Formulaic, but within the formula there’s a fair amount of variation that keeps the books interesting. Strange deaths, hidden motives, eccentric Britons–Agatha Raisin encounters them all (and Penelope Keith does all the voices, a huge plus for long car rides).
Bottom line: I’m never bored when reading an Agatha Raisin novel, and frequently I’m entertained. But her terrible taste in men drags down the entire series.