I had fun with NV, jsut after I did everything I ran out of things to do.
But even so I think "everything" for New Vegas is bigger than "everything" for Skyrim. New Vegas offers more quests (hand-made ones) and the RPG elements mean each character feels different, so there IS incentive to replay the game, support a different army and focus on different perks and unique weapons.
And hell one could even make the argument that "everything" in FO3 is bigger than "everything" in Skyrim.
New Vegas did an excellent job in story writing, RPG elements, character balance (YES, you do want character balance, even for single player RPGs. It extends replay value) and NPC depth/interaction, particularly with the companions.
FO3 did an excellent job with exploration, providing action and combat, and making the world feel dynamic.
While both of those provide very strong tools and exceed at what they're good at, Skyrim seems to fall flat in all-of-the-above. Not to say that Skyrim is particularly bad at all of those, but that it seems to
not be as good at any of those as FO3 and New Vegas were, which is disappointing.
Maybe Dawnguard will improve on this. I mean hell, it looks like we at least get to make choices with consequences there.