Film audiences seem to want 'a point', even if the point is that there's no point (as in 'Hidden'). Novels can end up with everyone going home and no great climax. Film audiences hate that. My motto is 'fiction is about the journey, film is about the destination'. In other words, the 'point'. In film, character is what character does. In fiction, it's often what the character thinks, rather than does. Usually, in fiction, the action is much more leisurely. Also, dialogue in fiction goes on for much longer and is often not very lifelike. Dialogue in film needs to be very life-like indeed. If you're writing a film, you really need to think in terms of a chain of events that cause the character to react in character, with each event causing the next, rising to a climax. Film audiences are perhaps much less forgiving.
A propos of nothing much at all. Here's a little pic of one of my young adult comedy novels by the way, Rude Health, a laugh-out-loud teen comedy about the Maths teacher from Hell , first published by Pan Macmillan, which was a Waterstones Book of the Week, and also included in a UK Virgin Trains Young Passenger Gift set. And because I'm a writer I cannot help but boast about the lovely reviews it got... Sorry! You have to boast about the good 'uns when you get them, and I really LOVE that cover.
'A truly funny book' The Times UK
'To laugh yourself stupid, pick up Rude Health' Girlfriend
'Linda Aronson is one of the best comic writers ... another first rate tale of a teenager in trouble' Daily Telegraph UK
'Fabulously entertaining' Achuka UK