I loved every campaign so far. The story is just amazing. Thats why i love the books so much (almost done with Evolutions.) I'm definatly biased toward this, but I like Halo 3s campaign the best, just because it is what got me into the series. It was the reason I got my XBox, and the reason I got CE, 2,Wars, ODST, and pretty soon Reach.
Also, Legends is out today. I'm going to have it in a few hours. Can't wait to watch the rest of the episodes. It is no where close to as good as the books, but still verry entertaining while adding to the universe (based on what i saw on Waypoint).