Personally I had a problem with the idea of Vaatu and the Dark Avatar. I liked Vaatu's design, and I liked he twisted eldritch designs of his dark spirits. He also had a pretty intimidating voice and goal (if a bit generic). The problem was that it kinda made me question the whole cosmology a little bit. Instead of being solely a spirit of chaos, he's portrayed as this God of Evil (I know that disharmony is considered Evil for the Philosphy Avatarverse follows, but there is no real "bad guys" side to things, as in it doesn't really connect to Unalaq's and The Red Lotus's point of view. If it can be believed that the oldest form of balance is chaos, then why are the Dark Spirits portrayed as so EVVVVVIL? Plus, after Korra destroys Vaatu there is still Disharmony in the world (Book 4). So that doesn't make sense as to how there still can be Chaos if he's gone.