Here is a link to the GameSpy interview transcript.
Changes to raiding
Tom Chilton: The feedback we've been getting has been overwhelmingly positive, as far as people really liking the fact that we're supporting 10- and 25-person raids.
Status of the beta
Tom Chilton: Finishing and polishing is really where we're at. The level cap will be bumped up to 80 pretty soon... We'll have Naxxramas in the hands of the players very soon. Wintergrasp will be fully playable for the players very soon.
Changes to class dynamics and new skills being added
Tom Chilton: For the Warlock, there's the demon form which is totally exciting... Knockback mechanics on various classes are exciting, like Thunder on the Shaman. The Mage's Deep Freeze should be a pretty interesting mechanic. We're trying to flesh out Arcane so that it becomes a very viable tree on its own as well...
PvP and competitiveness
Tom Chilton: Obviously we're trying something new with Wintergrasp... We're not changing the philosophy of the game itself. PvE is a huge, huge part of the game, if not the biggest part of the game.
Vehicle combat and what allowing vehicles has opened up in terms of PvP and PvE
J. Allen Brack: The team has just gone berserk with using the vehicle tech in all kinds of crazy ways. There's one quest where you drive a shredder around a field of scourge that's mobilizing. You take out guys twenty at a time, and just emulsify them...
Continuation of humour
Tom Chilton: ...we can't suppress our own sense of humor.
Death Knights -- dark and gritty
J. Allen Brack: In the case of the Death Knight, you actually start out as an agent of the Lich King. You're an evil person, you're a bad guy... you're going to complete quests that might make you a little queasy.
Further development of Warcraft lore
Tom Chilton: It feels like there's more depth to the lore in Lich King... aided by the fact that the storyline is one that's been forming since Warcraft III: The Frozen Throne... it's very rooted in traditional fantasy.
Recruit-a-friend and zerging through old content to prepare for WotLK
Tom Chilton: With Wrath of the Lich King, we're speeding up 60-70... we feel like our quest content from 70-80 is a lot stronger. Even outside the experience standpoint, we'd rather get you to the better content more quickly.
Revising old content
Tom Chilton: We did something like that [revising old content] with Duskwallow Marsh, adding new content there. We plan to do more of that.
J. Allen Brack: Heroic Scarlet Monastery and Heroic Molten Core are two of our biggest requests. Heroic Deadmines would be good too.
Gaiwyn of Proudmoore