I am an unashamed Bertie admirer. I only just read the latest as I knew once I'd read it I'd have to wait for the next one!
They are so well observed and the fact Bertie is more sane than his psychiatrist. And his mother parenting on a sort of belief system that totally disregards the character of her son and husband. The descriptions of Berties "alternative" school friends always has me smiling and grimacing by turns, particularly the ghastly Tofu!
I thought it was really touching when Bertie stayed in a "real boy's bedroom", and got a pen knife and how thrilled he was at that one short evening.
I thought it interesting that A Macall Smith said Bertie can never reach 7 because the poignancy of his situation is that he is six and so dominated by his mother, and that is the situation he explores.