I guess the reasons I love this book are summed up more eloquently by said publisher, thus:
...you feel yourself caught out of an abominable wicked world, crawling with selfishness and reeking with base passions, into one where there is much weakness, many mistakes, sufferings long and bitter, but where it is possible for people to live calm and wholesome lives; and, what is more, you feel that this is at least as real a world as the other. The kindly spirit which thinks no ill looks out of her pages irradiate; and while we read them, we breathe the purer intelligence which prefers to deal with emotions and passions which have a living root in minds within the pale of salvation, and not with those that rot without it.
It's moral but never preachy, funny but never sophomoric, observant but never cruel. The heroine, Molly, is quiet and studious, and always strives (often with difficulty) to control her temper, think well of others, and do the right thing. I'm tired of heroines whose utter lack of tact and self-discipline are upheld as virtues. Please. Give me more heroines like Molly, and more books like this one.
Age I'd let Z read it: As soon as she thinks she's ready for a book this long. I can't say for certain since I first read it in my early twenties, but I suspect this one improves with age and experience.