I saw Harry Potter and the Half-Blood Prince on opening day with five kids, ages 12-20. They all agreed that HP6 is the best yet. The rating is back to PG and there is more humor than in the past two movies. There were several times when our entire group was laughing out loud. The humor is more personal than situational, revolving mostly around Ron's hapless love life.
Fairly true to the book, even our most avid fan (dressed in costume), didn't complain much about missing scenes. However, if you're looking for Bill Weasley and Fleur Delacorte, you won't find them in HP and the Half-Blood Prince.
I loved the casting of Luna Lovegood and Bellatrix Lestrange, and they were awesome again in this movie.
Of course, they're already asking to go see it again, and we probably will. A great movie - worth the wait.