I feel i should explain why i feel it was a letdown, i didn't want to go into specifics when i started the thread because i didn't want to ruin it for people that haven't seen it!
Firstly they did not explain that Bill Weasley was engaged to Fleur, which is a pretty important thing to omit seeing as it is as their wedding that the death eaters attack in the final book.
They also decided to leave out the fact that Tonks was pining for Lupin and that they do actually become a couple towarRAB the end of HBP.
They do not mention Sirius at all, they don't mention that Harry was left everything in his will, including Grimwauld Place, which is where he hides out in the 7th book!
They miss out the bit at the end where Bill is attacked by Greyback
They do not explain that Harry and Ginny enter into a relationship which is KEY for the 7th book.
They do not show Narcissa Malfoy very much even though she is key to the book!
They missed out Dumbledores funeral.
Voldemort did not feature ONCE!!!
They missed out the relevance of the cave where the horcrux was, they didnt mention that Voldemort tortured those children there and that was how he managed to create the horcrux
In fact they just spent the whole film trying to turn Ron and Harry into these hearthrobs, which they clearly are not!
Hermoine spent the whole film pining after Ron, Harry after Ginny.
And they added that ridiculous scene where Bellatrix blows up the Burrow just to create a bit of drama!
It was a pathetic attempt at a romantic comedy, something HBP is not!
It was a complete disappointment!