I liked the episode and certainly want to see more about where they take it during the season. I did not mind Mulan, whom I really don't know much about, but I new she was going to be around this season. So is Lancelot, who is hardly a fairy tale character, but is a storybook character and one who has at least a partial real life counterpart.
I honestly did not see the wraiths as Harry Potter dementors because wraiths have been part of the fantasy world long before Harry Potter was written. Lord of the Rings is a good, but far from the only, example of that.