The just-completed third season of Game of Thrones is the most-watched HBO series since the fifth season of The Sopranos, according to Vulture.  The trend has been apparent for a while (see "'GoT' Passing 'True Blood'"), but the completion of the season makes it official. 

An average of 13.6 million viewers watched each episode of the third season of Game of Thrones, a combined total of initial views, repeats, DVR views, On Demand, and HBO Go. 

The final episode of the season also set a new record for a BitTorrent swarm, with over 170,000 simultaneous people active on a single torrent, according to TorrentFreak.  This breaks the old record of 144,000, set earlier this season (see "'Game of Thrones' Breaks BitTorrent Swarm Record").  The episode was downloaded over a million times in the first 24 hours after it aired.

Ratings were up around 30% over last season, and if other slow-building series are any indication, Season 4 of Game of Thrones could end up as HBO’s top original series season of all time.