Okay, so since nobody has really given it a proper review on this thread, and it seems like everybody who HAS said something significant about this has read the book, I thought I would put in my two cents...
First off, I'm more of a Lord of the Rings guy - so only with Prisoner of Azkaban did I get interested in Harry Potter. As a film, Azkaban was great, however, as an adaptation it was mediocre from what I picked up with my skim-through of the book.
I read HP 1-3 AFTER seeing the third film, therefore I've been to every Harry Potter film with a clean slate. Like I said, I was really into LOTR the three years it was in theaters.. I saw the first two films before reading the books, and read Return of the King before seeing the film. In a way, I regretted reading the book prior to seeing the film because I nitpicked the entire film, searched for inaccuracies, and overall just tore the film apart for its differences and injustices to the books, and in the end didnt like the movie until I saw it again and went in watching it as a movie, not the book.
Therefore, I didn't read Harry Potter and the Goblet of Fire before seeing this movie. I know the first three films have had their fair share of glaring differences from the books - especially with certain things that may not be of significance in that particular movie/book are cut out and end up having a larger role in the next book.
I went into this movie not knowing anything except the vague hints at the plot from the trailers and tv spots.
That being said, as a peice of cinema, this film is fantastic. There is very little down time and you really do lose yourself in the movie. At times, things feel a little rushed while other things (the dragon battle on the roof of Hogwarts) feel too long and unnecessary.
This movie is certainly darker, creepier, and wildly intense at times. It's definately a much more interesting and immersive movie-going experience than the past three films, especially the first two (which I was not a fan of at all).
However, I have major issues with the screenplay. It's weak in places it should be strong.
Neville Longbottom's issues with the spell on the spider was lost on me until I asked a friend, I just didnt get it. Also, I found other things confusing as well, such as the whole Barty Crouch and Barty Crouch Jr ordeal - what a messy muddled plotline that the writers could have made stronger and easier to understand with some work.
Also, the climax of the film left me a bit underimpressed... It was good, but somehow just not as climactic as it could have been... IMHO.
There were some other things the film could have been stronger with, but off the top of my head I can't think of it.
I felt like this movie catered much more to fans of the books and those who might not have read the books were lefet out in the cold when somethings came up. Probably not the best move for the movie, but its understandable since the majority of the Potter fanbase have read the books.
In all, fantastic movie, but with a somewhat weak screenplay.