The trend of retelling old stories to make well-known villainous characters into more sympathetic antagonists is not really new (see John Milton's take on Lucifer in "Paradise Lost"), but it seems that ever since Gregory Maguire's "Wicked" novel, we've been seeing a lot of movies that turn classic villains into misunderstood protagonists, or even transforming them into dark heroes.
Like "Wicked", "Maleficent" does a fairly good job of creating a more sympathetic character out of the villain: in particular, her motives for placing a curse on an infant are no-longer quite as trivial as a forgotten party invitation. While I loved first half of the film, which focused on the back-story of Maleficent and created a much larger world from the old Sleeping Beauty story, much of the ending kept me in constant eye-roll mode.
After creating a more complex, morally ambivalent, and interesting Maleficent, it felt like the writers just traded one villain for another by putting the black villain hat on a different characer
(in this case, the head of Aurora's father, the king), which felt a bit lazy to me. Much like Disney's earlier film "Oz, the Great and Powerful", their reliance on pat resolutions creates a weak ending, resulting in something that feels like a bad fanfic.