*deep breath*
My opinion? I loved it, yes, but I expected a lot more from it. I'll agree with Mystica that the direction was shoddy, but then again, I watched it in the crapiest cinema on earth, and there were some cuts that I am pretty certain WASN'T in the movie, and it was just the cinema being crappy.
The special effects were breath-taking.
I had already steeled myself for the fact that the Quidditch World Cup is just a breath, and that there were no creatures and no house-elves, so that didn't disturb me as much.
What I WAS disappointed by, though, was the lack of Ron/Hermione-ness in this movie. In GoF, as a book, it's the turning point of their relationship - there was simply no evidence of this in the fourth movie, except the haphazard Ron-jealousy thing. I was SO looking forward to the "you're fraternising with the enemy!" and post-Yule Ball fight, but it was nothing worth talking about. It seemed pretty much a mockery of the real thing. It was really just slapped together, and that annoyed me. I went along with my friends and they commented as well that the movie didn't reflect the book in the Ron/Hermione aspect.
What totally impressed me were the special effects, ESPECIALLY with the dragon and the piece at the stadium in the QWC - that stadium thing was SO cool!
Voldemort sent chills up my spine. That cinema is freakingly hot, but I felt COLD when I saw Voldemort. The scene where Harry returns to Hogwarts after the Triwizard Tournament was really powerful, I totally felt it there. But I didn't cry. It was really powerful and nice, but the way people were raving about it, I expected more out of that scene.
All in all, I guess all of my disappointment was due to over-expectations.
BUT I STILL LOVED IT.
It was better than PoA, in any case. But still, there was SOMETHING that Chris Columbus brought into movie one and two that unfortunately Alfonso and Mike just couldn't deliver. What made GoF (movie) so thrilling was, actually, the plot - and JKR receives all credit for that, not Mike Newell.
So it was a good film, I enjoyed it, and I was a bit hyper after I got out of the cinema. I'm sure I'll find it better after I've watched it in better quality (honestly, that cinema switched HP to black-and-white for a minute before it went back to colour! Who can take THAT?)