[Lord Aquaman]

The first couple of books had tight, simple plots that translated pretty well to the screen. Goblet (the film) suffered because, although they were things that were ultimately non-essential to the plot, a lot of what was cut constituted what created a lot of the flavour and atmosphere that made the book what it was. The books just get more and more unweildly from here. Likes been mentioned already, the next one will be a nightmare to get straight, and runs the risk of just being dull as a film.

Maybe they would have been better off being done as TV miniseries instead of 2 hour films. Then again, you wouldn't generate any merchandise and it would probably look absurdly fake even by bad CGI standards.