The visuals. Hogwarts come to life.
-Most- of the cuts were of things we really didn't miss. The house-elf stuff doubly so.
The Return (and consumate mourning)
The way the Polyjuice was handled. Sublte -and- cool.
The Quuddich game -- what we saw of it, anyway.
Hermione's set down of Ron. Also, her ball appearance.
Myrtle. She was so cute.
The "entrance" of the other schools. Sure, they showed a lot of it in the previews, but not all, and it was very pretty.
Damnit -- Bernie (fake Moody) should have gotten his say after he was captured. That was one of the best parts of the book -- the fanatic showing his contempt of the mere supporters.
Dumbledore. So flat. Not warm. Not in control. Not imposing. Not Dumbledore.
The costumes. wtf? Since when do Hogwarts kids wear school uniforms instead of robes that just -look- like school uniforms? Ron's dress robe just made this more painful, since it reminded us of the robes they weren't wearing.
The houses. You might be able to tell Cedric's house on a third viewing, if you hadn't read the book. I'm more skeptical about being able to tell Cho Chang's.
Viktor Krum. Wasn't he supposed to be Eastern European -flashy-, not strong and silent? He's a bit big to be a seeker, at that. Still, it worked well enough.
The Dark Lord. So ugly. I'm hoping he'll have hair in later movies once he's taken a chisel to his features.
Wormtail. Um. Yes.
Oh, we saw TG, TB, & TU a few weeks ago. Perty good, if a bit slow for a modern eye.