The impression I got from the film is that the Necromancer is a relatively new thing, and Gandalf first hears about him from Radagast/the White Council. Yet, in the books, he was very familiar with the whole affair and expressly tells Thorin that he found Thrain in the dungeons years ago, when he gives him the map. Not only that, Thorin has heard of the Necromancer as well, and asks Gandalf "what were you doing in that place?" with the implication that he has a well-known and unpleasant reputation. I also think they overplayed the corruption of Saruman at this early date.

On the other hand, they set up the influence of the ring on Thror fairly well.