I thought it was fantastic.
In fact, I liked it so much I'm going again tonight!
I am not a Harry Potter fan so I don't approach the films from a fannish or puristy perspective at all. I simply enjoy them very much as films. I couldn't tell you where the film of OotP differs from the book - I did think that some things in the story seemed to get very hasty treatment.
But overall I was bowled over by the style and atmosphere of the film. It's tense, exciting, emotional, and the battle in the Department of Mysteries is just FABULOUS!
I loved the first 3 books, thought they were delightful. Felt that JK was losing her magic touch a bit in the fourth. Fifth - OotP - bored me to tears. Half-Blood Prince was a huge improvement and recovered a bit of the old magic. Looking forward to Deathly Hallows like fun, but will be amazed if JK can tie up all those loose ends she's left dangling from other books.
Loved Luna in the film. Loved Tonks. Loved Helena Bonham Carter as Belladonna (looking forward to much more of her in HPB).
Gary Oldman gives a lovely performance as Sirius.
There's not enough Snape in the film, but then there never is.
I love Snape!
Young Dan is excellent. So is Emma Watson. There's far more chemistry between those two than there is between Film Hermione and Film Ron.
Enjoyed the Harry/Cho interlude. Muchly.
Young Dan is, to be frank, quite the dish.