Thrillers/Mysteries: Read Book or Watch Film First??

I have a question for you fellow avid readers out there:

What is your opinion about reading “thrillers” (and by that I mean fast-paced books with little mysterious twists and turns) after having viewed film adaptations of said “thrillers”?

I ask because recently I have watched the three films based on Stieg Larsson’s Millennium trilogy (after awhile I didn’t even really notice the Swedish with English subtitles 🙂 ) While I found the movies to be great and loved them, I have very little desire to read the books. And I think that is due to the fact that I know everything already. In the past I have loved thrillers, like the DaVinci Code books. I read the books and then viewed the movies and there was no problem. But I think I would have more interest in reading the Millennium trilogy if I didn’t know who would try to kill whom and when certain people would die.

What are your opinions or thoughts on first reading or movie-watching thrillers (or even just mysteries)?

I think, in the future, I’ll read first. (It probably would’ve helped if I had known going into the books/movies that they were of the thriller nature 🙂 Should’ve done more looking into them…)