well fnv has a lot more questeses
and it's all very interconnected
fo3 not so much, but the lore is as deep even if the quests don't all link up somewhere unnoticeably specific

It's the nostalgia... at least for me. I still love FO3, but NV is more refined in many ways.

I do prefer the urban environment in FO3 rather than the western crap in NV though... they kind of went overboard with it... just a wee bit...