The later films aren't dark

aesthetically they might be, they look murky. However, in terms of character,themes and content they are no darker than Columbus' effort in COS. GOF might look dark and gritty, however the characters and plot are extremely infantile. The film is lacking in development taking away much of the seriousness. The actions scenes may be long but they cut out most of Rowlings darker content (Crouch Sr. Insanity, Barty Crouch Jrs story) the comical approach to the villains also shows a lack of maturiy, indeed we are essentially watching a children's film trying to pass for a darker, fantasy piece. OOTP is no better the blue filter, the very deep blackness in scenes (it is very hard to see in the Ministry of Magic) all these visuals are taken down by the lack of any real threat of danger, Umbridge is a caricature in the film whereas she was a vicious nazi-like control freak in the book. Much of her sinister nature has been lost. The character are all very static and seem more or less just there they do not grow at all throughout. HBP so far has been the ultimate, aesthetically it looks murky and grim but the content is not. Much of the characters still feel extrodinarily shallow compared to the book, and most of Rowling deeper, sinister content as been lost in place of more visual ''darkness'.

POA is still, by far, the most mature. Visually it is a dark piece but Cuaron gave it the content to back up. Thre film has a CENTRAL theme, that of family, which is worked masterfully into the picture. Neither Yates or Newell did this leaving their films lacking depth. The characters also grow and develop much more in this film they react to the events in a very realistic manner, giving the film a much more grim touch. Cuaron kept the darker elements of the book (Harry swearing to kill Sirius, handing Pettigrew to the Dementors) and that amplifies the seriousness of the story.

DH, going by the previous efforts on Yates' part, will look 'gritty' but the deeper points of the film are unlikely to reflect that. His character have so far been surprisingly underwhelming, reacting very unusual in certain situations. He can add all the visual elements he likes but if the films characters and content do not go deeper then it will fall flat, rendering the whole film very basic and unsatisfying.