Surprisingly, I went to the theatre with my family.
My brother, who would sneer at me if I talked about HP in his presence three months ago, persuaded me and my mum to accompany him to the theatre. I'm glad I went with him because I really enjoyed myself, even though GoF lacked the magical touch and atmosphere of PoA (Hogwarts felt more like an ordinary Brittish boarding school and less like Hogwarts).
I liked almost all of the changes they (Kloves?) made to the plot and the special effects looked great on screen. With one exception the actors were marvellous, especially Isaacs (it's such a shame he can't have more scenes in the movies). And I was pleasantly surprised how well all all the teen-age romance was portrayed. Oh, and Filch got so much space! He was closer to Ozma's Filch than to Jo's, though.
However, several things didn't work for me: In PoA I believed Gambon's performance, his Dumbledore was the brilliant but mad headmaster I imagined him to be, but here in GoF he was merely a woried old man who happens to be in charge of Hogwarts. This time around he had no authority of his own, only the authority of his office.
Second thing that jarred with me was the cutting. It was often too abrupt, in particular I wasn't prepared to come from Snape's stock room to the third task.
And lastly, why was Voldemort's rebirth witnessed by only seven DEs? It was all dark and scary - I expected Voldy to be encircled by his true family.