On the whole matter about what Obsidian is and isn't really changing from Fallout 3, I'm actually pretty happy about it. From what I'm hearing, at least. I'm glad the gameplay isn't changing much. I like how it's not turn based, or 2D/an isometric view. It feels less separated from reality than when it's 2D and such. At the same time, I'm also glad that Obsidian has changed the way they do the story, dialogue, etc.-from what I'm being told anyways. I never played the older Fallouts, so I'm sort of 'taking a leap of faith,' on the subject. I guess.
Of course, there's more to gameplay than if it's 2D or 3D/turn-based or real-time, but nonetheless.
Still, it has thus far sounded as if they're taking the best from the previous games. If that's true, the next game should be great.