While we're getting a lot more Necromancer background in the film than was in the book itself, I can't help but feel the Necromancer / Dol Guldur storyline has been way over simplified: 900 years compressed into one visit by Radagast!
Maybe more will be revealed in the other movies (after all, the third movie was supposedly justified by all the additional stuff that could be told linking The Hobbit and LOTR).
UPDATE after seeing DOS: there's more development of the Dol Guldur storyline in the second film.