I have really enjoyed all the Donleas I've read so far - they're fairly quick reads, the plot keeps moving at a good pace, and so far none of them have fallen into the bad plotting trap of a totally out of left field killer (I feel like for these sorts of thrillers, a reader should be able to figure things out along with the main character, so the resolution shouldn't be a 100% complete surprise).

Just FYI re: Maggie reading them, Twenty Years Later does have some referenced kinky-ish sex; it doesn't happen on-page but there's a videotape that characters watch/discuss.