Gamer Syndrome has put together an editorial that briefly profiles Obsidian's Fallout: New Vegas, Interplay's Fallout Online, and Bethesda's as-of-yet unannounced Fallout 4 before offering some speculation about the titles. Prepare yourself for a grammar crash course and plenty of inaccuracies:
The fact is, that Obsidian aren't Black Isle. They may be the same people(at most) but they aren't Black Isle. That doesn't mean they're bad they have proven it with KOTOR 2 and Neverwinter Nights 2. The second thing to be take into consideration about New Vegas is the fact that Bethesda won't let Obsidian do whatever they want, and we'll likely see Fallout 3 in Vegas. I sure hope i'm wrong, but odds are we will.
Next is Project V13. The fact that the game is an MMO immediately turns into a disadvantage. Lot's of fans won't even try it or even be able to. Also, when was the last time an original MMORPG was released? Guild Wars. Yeah, that about does it. Also, Interplay are working on the game which means that it won't be created by the original developers. We'll have to wait and see.