Zhaitan has amazing story against his Risen. The Risen has a very strict structure with many champions and cunning tactics. The whole war was epic but the dragon itself's fight was terribly done.
Mordremoth had some interesting twist and a fine battle if we put the bugs aside.
Kralkatorrik itself had a lot of screentime but his minions were very poorly done compare to Zhaitan and Mordremoth.
Primordus' destroyers were hive mind army as it was shown in GW1.
Jormag was interesting, we saw a lot of his manipulative personality in the novels but the dragon itself and Drakkar hasn't shown up yet. He also has a cult following him.