I loved Agatha Raisin when I first discovered her. The first few books are really addictive. The later storylines got even more ridiculous and even more silly. In the same vein as Hamish Macbeth, M C Beaton gets away with it because you, as a reader, become fond of the characters and so when another book is churned out, you instinctively hope that maybe something good has at long last happened to the main character and so your loyalty hasn't been in vain, unfortunately as with Hamish Macbeth this never happens and you get to the end of another book saddened that you cannot get that time you have just invested, back again.
I love Agatha Raisin and some of the main characters but my advice is the same as I would give about smoking, don't start because its really hard to quit.