The story line has been described several times, so it's not worth
repeating. The book seems very introspective, even for Maugham.
However, there is enough happening, that one does not loose
interest. While I can't claim to understand Kitty, and neither does she seem to
fully understand what happened to her by the end of the book, the
story drew me in. Kitty changes so dramatically over the course
of a couple hundred pages that her internal struggles are probably
more gripping than the description of the turmoil around her.
While Maugham could write excellent short stories and short novels,
I did enjoy his longer novels the best. While the "Painted Veil" is certainly
worth reading, it simply doesn't have the scale of those longer works.
Therefore a comparison is probably not fair.