My problems with this films are as follows:

Rating: 3/10 (11 November 2007)

1) Comic relief The line, "I don't want my brother coming out of that bathroom with nothing but his dick in his hands" from The Godfather, apart from being a seemingly out-of-place humorous line, helps us to identify with the character and underscores the tension of the scene.
Granted that you can't compare The Godfather to Harry Potter, but this does illustrate how badly comic relief was handled in OotP - it is used in almost every scene in the film, and makes it impossible to take many of the villains, and in fact much of the film, seriously.
Example. When we're given a scene where Umbridge is giving a negative assessment of Trelawney's teaching skills that is clearly presented in a comedic fashion, it makes it impossible to empathize with Trelawney for being fired almost three minutes later.
In fact every scene involving Umbridge, Malfoy, Fudge, or any other antagonist is injected with comic relief, usually in the form of deliberately exaggerated acting or slapstick. But then again, if seeing Filtch sitting at a fold-out table eating an American-cut ham sandwich waiting for the room of requirement to open doesn't impede on your ability to suspend disbelief, then be my guest.
2) Time budgeting.
I'm hardly one of those fan boys who picks apart every scene from the book that didn't make it into the film, but given that we've seen the longest book made into the shortest film, I'm not going to accept it when major plot points are eschewed to fit in twenty-five additional minutes of meaningless banter.
Example. Given that the "Snape's worst memory" scene is debatably the most powerful scene in the entire series, would have killed anybody to devote thirty seconds of screen time to it rather than ten? Scenes with the kids hanging around in their dormitory listening to Rooney seem to never end, but the climactic scenes go by at such a fast-forward pace that if you turn your head and cough, you will miss at least several important occurrences. Given that if the film had even been as long as what was previously the shortest in the series this could have been less of a problem, there is no excuse.
3) Actual budgeting.
In GoF, we get an extremely visually compelling scene in which Harry talks to Sirius through the fireplace. We see a pile of ashes and embers start to mold into a human face until they vaguely resemble Gary Oldman's. In this film, for the same scenario, we see Gary Oldman's disembodied face floating around in what could have been a tenth-grade graphic design student's submission to Youtube.
Oh, and why does Grawp look like George W. Bush? In conclusion, this doesn't even need to compare to other actual films for it to fall flat, all you need to do is compare it to earlier entries in the series to see that it doesn't hold up in any way. Compare any actor's performance here to their performance in a previous Potter film (the flat of direction), compare the special effects, the costumes, the way the subject matter is treated, anything, and this film comes across as amateurish, hurried, and impotent. The fact that this same director has already signed on for HBP proves that Euripides was a very wise man.