I haven't read any of the Harry Potter books. Just so you know.
I heard, anecdotally, that fans of the book were not happy with the movie, so I didn't expect much. I ended up liking this installment the most out of the series.
By now, everyone knows what the plot is about: Harry Potter (Daniel Radcliffe) is entered into a contest deemed too dangerous for boys his age, the Tri-Wizard Tournament. Two other schools are invited to participate--near as I can tell, they're French hot girls and brutish Russian guys--giving some much needed variety and depth to a world that's mostly taken place in a stuffy little school.
A lot has changed. We have a new Master of the Dark Arts, Alastor "MadEye" Moody (Brendan Gleeson), with magical eye patch, mechanical leg and all. Albus Dumbledore (Michael Gambon) finally starts acting like a person instead of a benevolent incarnation of Father Christmas. He gets mad, he freaks out, and he sometimes appears to be a big hippy. Heck, even Rubeus Hagrid (Robbie Coltrane) gets a little romance.
Speaking of romance, the movie doesn't focus on the character interactions so much that it feels like we're watching a soap, and that's a good thing. Mostly, it's the awkwardness of learning social graces that terrorizes our poor students. You know, the things that haunted the geeky among us to this day: asking girls out, wearing "cool" clothes, knowing when to dance and when not to dance, and discovering your female friends are becoming women.
The terrifying trials that constitute the Tri-Wizard cup keep things moving. Behind it all is that pesky Voldemort (a marvelous Ralph Fiennes) who breathes life into a villain who has been entirely two-dimensional for too long. Not any more!
Even the special effects have been upped. Kids on broomsticks no longer look like bad CGI. The dragon battle even looks fantastic. In an age of Lord of the Rings, that's saying something.
What was most satisfying to me was the feeling that Hogwarts is now a real school. Teachers worry about students getting hurt (there's an age limit on the Tri-Wizard Cup for a reason), argue over disciplining their charges, and fret about teaching styles. This is a real school with real problems, even if they're magical problems.
That said, the movie occasionally sacrifices rationale for speed. At one point, several characters are intentionally placed in grave danger as part of the Tri-Wizard tournament and everyone's supposed to be okay with it. Unfortunately, that kind of contest cheapens the tragedy of loss felt later--it's hard to muster up tears when someone gets hurt after Hogwarts basically kidnaps its own students in the name of competition.
Still, it's a forgivable quirk that my wife tells me is explained in the novel. With all the action, crazy characters, and burgeoning relationships, Harry Potter has now moved into the realm of adulthood. Maybe that's why I liked it so much.