The first two hours were pretty enjoyable. Well worth waiting for.
But the ending ... what was up with the ending? It's like going to a fireworks show, expecting a blazing finale, and getting ... two guys with sparklers.
I'm OK with "suspending disbelief" while watching movies. Especially with movies like these: it's part of the deal. I'm OK with the compromises and changes necessary to bring a book to film. But the book ending is such a brilliant combination of emotions and adrenaline, yet the movie just sort of fades away. "Please." bang. Walk away. Break a window. Cast a couple weak spells. Harry just stands there, and the rest of the school is empty. Dead ... like the ending.