It has a lot of answers, few weaknesses, and a combo that's nearly a OTK from full life. I worry that it will get even worse with a few of the previewed cards, psychic scream being a large offender.
They have early game removal, massive board clear, spot removal, Shadow Visions helps ease the Highlander drawback. It's just a matchup that is incredibly hard to tech against or even build a specific deck to fight. It's also a large % of what you see in the ladder.
I love Priest and it was always my favorite class (because of the Dragons theme) however i really hate the current Priest because everybody plays either Big or Highlander Priest, both are 100% high roll decks who don´t require much braincells to win (that´s what high roll stands for). It´s just not fun to play against (like most current meta decks).
Next expansion you'll be happy with Dragon priest again... except that it'll probably be weak against Big and Highlander. But it should roll nice against other classes.