The Elder Scrolls V: Skyrim's Lead Artist on Dawnguard's Size

During a still-unpublished interview with GameFront at E3, of which a tease has been published on the website, Bethesda's lead artist Matt Carofano commented on the size and amount of content of Skyrim's first DLC, Dawnguard. According to him, we won't get something as extensive as Shivering Isles for Oblivion, but it will still be larger than Fallout's and Oblivion's other offerings:
(It'll take between 10 and 20 hours to beat,) Skyrim Lead Artist Matt Carofano told Game Front during an interview at E3 2012. (It's about as long as a faction line.) So about as long as the Mages College or Companions Guild quests

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You'll also get sent to one of the planes of Oblivion, the Soul Cairne. The Elder Scrolls IV: Oblivion also sent players to a different plane in its expansion, The Shivering Isles, but don't expect the Soul Cairne or Dawnguard to be quite so extensive as that.

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(Dawnguard will be significantly bigger than any Fallout DLC,) Carofano said. (We wanted to do something more in depth than that. It's not as big as Shivering Isles, but there's still a lot of content there.)