I hated the bullshit they came up with the Witch-King being sealed in a tomb or something then breaking free. He simply escaped the final battle in Eriador after taunting Earnur and hid in Mordor until the LOTR events took place. Otherwise, the movie is great. But there are unnecessary changes to some details that bothered me.
Sort-of. Sauron himself was inhabiting Dol Guldur and Mirkwood under the guise of the Necromancer. While it's said the Witch-king was in Mordor rebulding Minas Morgul and Barad-dur, the seat of Sauron's power, it's not unwarranted that he went between Mordor and his master. The bigger point they were making in the scenes with Radagast was that Sauron, a.k.a 'The Necromancer" was in Dol Guldur.