The only expansion I played in FO3 was the first one, and it was ok.
I have come to the conclusion that, shock of all shocks, I'm a Bethesda fanthing. I like big open worlds where I can just wander around and do shit. Fallout 4 is probably my most anticipated game since Diablo 3.
I had a hard time getting into New Vegas... spent about five hours playing it and it just didn't click. It's going on my BACKLOG'N list of shit that I'm gonna catass between semesters starting next weekend, though.