Fallout: New Vegas - Interview @ Shacknews

Shacknews has the first interview on Fallout: New Vegas, with Pete Hines saying they "tried very hard not to put much in the way of parameters on them":

Shack: What has Bethesda's attitude been in terms of allowing Obsidian freedom to create their own Fallout game?

Pete Hines: I think we tried very hard not to put much in the way of parameters on them. To let them kind of come up with the idea. So we didn't go to them and say, we want a game that is set here, and--we didn't do that. We said, "What would you do with it? If we were going to do this, what would you guys like to do?"

Shack: So you asked them for a pitch, as opposed to pitching them a project.

Pete Hines: Correct, correct. And honestly, generally speaking, that's how it works best, which is: you've gotta have people who are really vested in the idea that it's their creation. "This is what makes us excited. If we could do this, this is what we would want to do."

You may help them mold or frame that, but if that's what they're excited about, then that's what you should do. As opposed to, I come up with something that would be cool, and you go to them and they go, "Oh, okay. Well, sure." You're just not necessarily going to get the same passion or excitement from the team. And those are the guys who need to be the most excited about it, because that's what they're going to go into the office and be creative on and make for the foreseeable future.

But it was good. I think we were all on the same page in terms of the kinds of things that we wanted to do, and what it could be. And yeah, so now I want to play it. 

According to an article from MCV linked at Blue's, the game will use the Fallout 3 engine but there doesn't seem to be an original source for this with commenters at Blues saying this was not mentioned at the original press event, so take this with a grain of salt at this early stage.