Now Greyjoy:
I don't recommend playing them: here's why.
(1) - One single card destroys a portion of Greyjoy's strategy: Brienne of Tarth. She disables saving, unopposed tech, and GJ's other schtick: canceling other people's triggered effects. Another takes out unopposed - Cat of the Canals.
(2) - The Laughing Storm, and Narrow Escape also undermine Greyjoy severely.
(3) - Targ hoses greyjoy. They can keep it from being winter (the one proven GJ Strategy as done by Dobbler), burn cancels most save (except Risen from the Sea)
(4) - Baratheon does saving and unopposed better than Greyjoy. Sorry but they do.
(5) - No in house draw that works, too expensive to rely on Val.
Not saying a good player can't do well with Greyjoy, but unless you really, really like them: don't play them. You'll just end up frustrated at the lack of any coherent theme, a large amount of cards and direction that goes nowhere. The crucial difference between Greyjoy and Stark/Baratheon is that the other houses have enough redundancy on winning themes to make up for less draw than say Lannister (which also has redundancy and gold) or Martell.
Besides, maybe if everyone stopped playing Greyjoy, Nate might get an idea that he has to revisit this house and make it playable (for people other than Dobbler).