Complex sentence: Bret Easton Ellis, who called the novel "Probably the funniest young-guy-in-New York novel since Bright Lights, Big City" is adapting the screenplay for a 2011 film starring Joseph Gordon-Levitt.
Split into simpler sentences: Bret Easton Ellis, who believes the novel as "Probably the funniest young-guy-in-New York novel since Bright Lights, Big City". He is adapting the screenplay for a 2011 film, starring Joseph Gordon-Levitt.