My wife had read the book and while she said it wasn't one of the author's best, it was good enough, so I gave this a go. I've found that sometimes weaker books from an author make better films than stronger ones, and while I was a little dubious of the subject matter, I thought I'd give it a go anyway.
What I got was a heap of fairly risible trash, with phoned in performances, some remarkably passionless bonking, a retread of the familiar "It's all a Catholic plot!" Grail stuff, and a curiously strong desire to persecute Cathars. Not on religious grounds, mind you, just for being annoying. It's a pain when you're several hundred years too late to join in the fun :(. I'm just rather disappointed, overall. It's full of actors that I like, so I disregarded the rather uncomplimentary heads-up from the Radio Times and plowed on with it, only to come out at the end with, well, nothing.