What appeals to me about Rendell's writing is the way she is able to convey sympathy and identification with her criminals by making you see the world through their eyes. She does this with an accretion of detail which, at the beginning of some of the books, is sometimes tedious, but which eventually is very suspenseful, because you know something is going to happen, but you don't necessarily know when or (sometimes) to whom. And it all unfolds before you and there is nothing you can do to warn the eventual victim.Despite my enjoyment of her books, it is a surprise to me so many of them have been dramatized because her plots generally occur over a long time and consist of conversations and interior dialogues which would be difficult if not impossible to convey visually; they would require narration, which is often awkward. GALLOWGLASS has quite a bit of narration and is not particularly enthralling compared to the book.
In addition, unlike most mysteries, there are generally not a series of murders in Rendell's plots; and the thrust of the writing is almost never to figure out who the murderer is. It is more about the inevitibility of a tragedy occurring which is often set off by something very minor but which builds and builds until the "straw which breaks the camel's back".
Information taken from http://www.cosmoweb.net/~foosie/rendell.htm. If you're interested in a list of books by Ruth Rendell, you'll find it there.