Overall, I enjoyed it. This one seemed a lot shorter than the other three movies, and I don't know if that's because of the pacing, or the director, or what. It was certainly a lot funnier, but that could just be because I have a filthy, filthy mind (about which more below).
I really liked how the effects were done, particularly the Dumstrang ship and the dragon.
Stuff I didn't like so much: Some others have pointed out that the happy-end seemed a bit too tacked on, and I tend to agree with them. In fact, the movie pretty much omits what I feel is a crucial part of the ending, namely Fudge's refusal to believe that Voldemort has returned, and Dumbledore's emphasis on the bonds of alliance and friendship. This, I think, is central to the conflict in the next two books, and so I'm a bit disappointed that it wasn't emphasized as much in the movie as it was in the book.
Now, granted, I can see apis_mellifera's point that in a screen adaptation, you need to get from point A to point B, and by necessity, you have to leave out a lot of material that works in a book but not so much in a movie. The emphasis on Fudge's disbelief works well in a book, but probably not so much in what is essentially a movie aimed to younger audiences. And anyhow, it was Mike Newell's choice to cut that stuff out, and it was a valid choice for him to make. So it's not like I'm going "OMGWTFBBQ the movie is RUINED!!!11two"
Now! Stuff I liked!
My mind went to a lot of very, very naughty places during the movie. Not least of which was the scene with Harry in the bath (shirtless!) and Moaning Myrtle putting the ghostly moves on him. Plus, the scene where Draco gets turned into a ferret, I couldn't help but think "See, now it's canon that Draco gets into Goyle's pants!"
(I know, I know, Special Hell, I'm going...)
Of course, there were a couple times with Fred and George that I just wanted to yell out "Twincest!", though I can't recall what parts they were. And the scene where Harry is being attacked by the grindylows, I wanted to yell out "Tentacle rape!!" My mind is a very bad place sometimes.
Dear George Lucas: There is a right way and a wrong way to have a character howl in anguish over the death of someone very close to him. Please note this movie, particularly Amos Diggory. No love and you owe me $6.50, Me.