Profanity: Better in everything except the engine. And I guess exploration, but to be fair, a lot of Fallout 3 exploration was based on going through a whole load of nothing.
Sachys: sounds bit like oblivion in that sense
They're really different: Fallout 3 is "choice-driven", meaning that the player is a sort of demiurge of the world of Fallout - what you choose will happen. This is interesting, because you feel powerful, but it has a negative effect on the whole game experience: you'll never be caught off guard, no dramatic turns of events, nothing at all. It is developed by Bethesda, and I think they did a good job in preserving the same feeling of the original games.
New Vegas is a real RPG, developed by Obsidian - with all the pro and the cons of Obsidian games, actually. Obviously, being the original developers of the Fallout series, the adherence to the original concept is even more marked in this game, and the story too is far better. You'll find more bugs, probably, even if I was able to play without problems.