There have always been books which forced the impression to be unfilmable. But then some producers, directors, and writers came and showed that the stuff is not unfilmable. We all know that the 'Lord of the Rings' franchise was one of these "so-to-say" big unfilmable ideas, but at the end it became a highly acclaimed movie series.
Which of these movies and tv-series that seemed to be unfilmable rocked it the most? (Or Which do you think will rock it the most? - For productions that are still not released.)