Over the last 12-18 months or so, it has become evident from tournament results that Lannister is dominating the large scale tournament scene. While not all metagroups may agree that Lannister is that powerful, I think the general consensus on these boards (and from tournament results) is that Lannister is clearly the strongest house. Last year at Gencon, nearly 50% of the field showed up playing Lannister. As much as I hate playing Lannister, I chose to play it at the Minnesota Mega Event since I felt it was my strongest deck.
We've already seen some errata (to Alchemist Guild Hall), but instead of recommending more errata or more bannings, I'd rather discuss what are the best methods for finding a way to beat Lannister.
One of the things that makes Lannister so strong is the repeatable control. 3x Castellan, 3x Flogged and Chained, Lannisport Brothel, and Alchemist Guild Hall form a strong backbone of cards that round after round kneel one or more of your characters until you find a way to remove that card. Add in one time kneel affects like Distraction, You Killed the Wrong Dwarf, Enemy Informer, and the City plots, and you have cards that provide "single-shot" kneel effects to pick off the characters not knelt by the "backbone", and including single shot discard effects like Varys and Arys Oakheart just adds to this effect. Lannister generally has enough card advantage to allow the "single shot" effects to do their job without feeling like they are card disadvantage, and they have enough Gold to offset the lack of gold provided by the City plots.
So what can we do in building decks to de-claw the Lion?