Though everyone likes to complain about Aggro Shaman, Dean "Iksar" Ayala, Game Designer at Blizzard has responded to a thread on Reddit about the existence of a Tier 0 zero, meaning one that was leaps and bounds above the others. According to Iksar, Undertaker Hunter pretty much falls into this classification.

In his post, which you can find below, he explains that the archetype made up almost a quarter of the meta at one point after Curse of Naxxramas. And as we said, while Aggro Shaman is the new thing people like to talk badly about, it's only half as widespread as Undertaker Hunter was at its peak. This is, of course, assuming Aggro Shaman is the most popular Shaman archetype as Iksar says, Midrange Shaman has been on the rise though we doubt it would take over the meta that quickly.

He also shares some other information including the fact that Druids had highest win-rate as a whole which was from early on in the Force of Nature + Savage Roar era.
Originally posted by Blizzard (View Original)Collapse

Number sharing time! As a single archetype, Undertaker Hunter was about 25% of the meta at one point. For perspective, the most popular archetype of Shaman is currently less than half that. Class win rate wise the highest overall number I've ever seen was Druid around 57%. The highest single player in Legend win rate (min 50-70 games single deck) was around 75%, it's usually about 70.

[The win-rate of Undertaker Hunter was] 55-57% if I remember correctly.
The intention wasn't really to prove any point, but just to give perspective on Undertaker Hunter popularity for people playing on ladder now. However, all of Shaman (every Shaman deck) right now sits around 19-20% of games, which is still around 5% less than the Undertaker Hunter solo archetype was.
He also takes some time to talk about the 45 cards removed from the Arena.
Originally posted by Blizzard (View Original)Collapse

We have the ability to look at card performance across all skill levels. None of the cards removed were strong at any skill level. Some of the cards removed were fun to play, but I think when you have to reach a critical mass of cards to remove, it's hard to avoid that. A great deal of effort went into choosing the right cards, but we're interested in feedback on cards you think should have been removed instead.