I haven't decided.
I loved Fallout 3, I played it to the fullest when it came out and even since it was released up until last month I came back to it.
But in saying that Fallout New Vegas looks and sounds the exact same as Fallout 3, and it could make it stale for me, I think it'll be good with Obsidians take on how Bethesda had re-vamped it but if the atmosphere and mechanics are the exact same it will be hugely disappointing for me.
So until new information on how it will be comes out along with videos and screenshots, I'll still be undecided.