[UPDATE - the service is now back up, we contacted Blizzard for comment on the reasons for the outage but have received no response yet]
Battlenet is having some serious issues today, with players unable to connect to the service in order to play Blizzard's range of popular titles. Though not entirely unknown, the service is generally relaiable and we've never seen such long queues to simply log into the service, taking around 15 minutes to simply get the game launcher up.
With other popular games, such as Destiny and Call of Duty, having suffered from DDoS attacks in recent days, it's suspicious that Blizzard is having such problems today. Though hacker collective Lizard Squad hasn't yet sent any message that it is repsonsible.
Other reasons could be a patch to Hearthstone that nerfs a couple of popular cards, Leeroy Jenkins and Starving Buzzard, though such patches haven't brought the service to its knees before. Blizzard itslef isn't being very helpful with no explanation on its Twitter feed , the US Twitter feed mentions routine maintenance, though that's not been noted in Europe, and we'd think they'd be quick to pinpoint that as the cause if it was.
We'll bring you more details as they become available.