Holy crap, I agree with nearly every single point iSM makes about a Harry Potter film and book. Wonders never cease.
You seem to have expertly covered everything, Steve. I'll just add that I think the movie improved on how Cho's relationship was handled, and I think it was more interesting (and sad/tragic) to have her betray the DA because of Veritaserum than it was having it be her friend... Plus, it eliminated how nasty Hermione was in the book by ridding itself of the curse Hermione used on Cho's friend - that never sat right with me.
And I totally dug the movie Gwarp. HATED that entire sequence in the book. Snore, snore, snoring.
And though I too missed the actually missed of the Department of Mysteries, I think on celluloid some of that stuff would have just looked cheesy. Whereas the wizarding battle once the Auror's arrived? WOAH. Way more fun to watch then read. Sirius decking Malfoy - yes! And since [SPOILER WARNING FOR DEATHLY HALLOWS]
Another side note spoiler for DH...
The acting was probably at its finest in this film. Definitely as good if not better than PoA and WAY better than Goblet of Fire, my least favorite of the movies.
Alan Rickman looked less like a grandma and more like the Snape I like to imagine. Naked. In my bed. With me also being naked. And in my bed.