5. The Dark Tower
One of the most grandiose book series ever written, Stephen King's eight volume saga takes up 4,250 pages and tackles a variety of genres. In 2007, JJ Abrams expressed interest in filming an adaptation of the series but he later withdrew. Afterward, an attempt was made to adapt the series using a combination of both films and a TV show. Ron Howard was set to direct with Javier Bardem playing the lead character Roland Deschain but negotiations with Universal Pictures eventually failed. After that Warner Bros. showed an interest in making the series with Russell Crowe as the lead but the project has still not fully materialized. While Ron Howard isn't exactly a knockout every time director, the series sounds extremely ambitious and would instantly become one of the more interesting series around if it could ever get made.