Two of my favorite books are Donnie Brasco and The Beach which in turn turned out to be two of my least favorite movies, adding a favorite of the last few years in Shutter Island doing the same with a bad movie version I always worry when something I like to read is being turned into a film.
I was, and still am, pleasantly surprised with The Walking Dead and Dexter, (Especially the early series,) and think for a TV show they need to eventually go a different direction from the source material to keep it fresh, so I think the Newsflesh trilogy could go that way in the same vein as Dexter and TWD.
In terms of movies, I'm still amazed that there hasn't been a version of Lord of The Flies that has been adequate. Maybe the fear of using child actors for the main roles has put them off, but the success of Beasts of The Southern Wild may change that. I honestly thought when Lost finished and was a huge success we would see Lord of the Flies in no time.