Oh gosh, I love Barbara Pym. That said, I didn't warm to her straight away. I came back to her after a delay of some years and then adored her. Maybe this is because I had become a more boring middle-aged person. But I hope not! 😂
It's true that not much happens in terms of plot. Her novels are all about the tongue-in-cheek observation of daily life, and human nature. There is often a single woman protagonist (a spinster if I can use that old-fashioned word) who wryly watches and observes everyone around her. There is also an amazing sense of time and place; you feel like you've stepped into the world of 1930s/40s/50s Britain.
I find her novels very restful when I'm stressed. Her characters worry about trivia, and we as readers can see that it's trivia, but they can't... it reminds me that the everyday stuff I get so anxious about in my own life is not actually that important.
Jane and Prudence isn't my favourite. And @terpsichore is quite right to say that Quarter in Autumn isn't like Pym's other novels. The protagonists are older, and the narrative overall is bleaker.
My favourite Pyms are:
Crampton Hodnet: satire of north Oxford, amazingly well-observed, and Pym wrote it when she was only an undergrad herself, which amazes me. It was published posthumously.
Some Tame Gazelle: Pym's first published novel. As so often with Pym, the male characters are comically self-important and the women see right through them.
Less Than Angels: a satire of academic anthropologists. Pym herself worked for years as an editor at the International African Institute in London, and she draws on her own experiences when writing this novel.
These are my favourites, but they're not necessarily her best; they're just the ones I loved the most. (I like academic satire.) What draws me to Pym I think is that she recognises silly human foibles so well, but doesn't necessarily condemn any of her characters, no matter how blinkered they are. She satirises them but also recognises their humanity.
Sorry for the long post; I'm procrastinating and am spending way too much time online at the moment...