From the official announcement:
Three new playable decks: Liliana Vess’s “Grave Whispers” deck, Ajani Goldmane’s “Auramancer” deck, and Ral Zarek’s “Cloudburst” deck
Six exclusive sneak-preview cards from the upcoming Innistrad expansion
Players can become the Archenemy in single-player and online multiplayer formats
Six new single-player campaign levels and eleven Archenemy single-player campaign levels
Four Archenemy challenges
Four additional card unlocks for all thirteen Duels 2012 decks
New achievements on Xbox, Steam, and PlayStation
New loading screens featuring art and text exclusive to the Duels 2012 Expansion
Much like the rounds of DLC for the original game, we’re seeing three new decks plus cards for the decks proper. This has quite a bit more “content” in terms of campaign levels, but they do not note if they are “puzzle” levels or “duel” levels.
The other huge news to this release is that you’ll be able to play “as the Archenemy”. Currently, you may only take on a computer Archenemy. This will be one of the big selling points to me, I love this aspect of the game.
The price was not announced, but I would take a guess and bet on it being close to $5 dollars, which is reasonable considering the content you’ll receive. They also did not note “when” it will be released other than “early fall”. Considering “Innistrad” comes out at the end of September, I would imagine we’ll be seeing it sooner than that.
You can find out more information and check out some screenshot here.