But lets take a lookie here:
NV is basically a port of Fallout 3 so your paying a new game price for a conversion of an old game.
It was released in a more bug ridden state than most Bethesda games and that takes some doing.
It uses an old engine that Bethesda never seemed to master, (even though the guys from Larian can make it hum along quite nicely).
I enjoyed NV a lot, but I did think it was a bloody cheek using the same old engine, assets and so forth and charging full price for what was a bunch of largely broken quests and unfinished AI. If I didn't already own FO3 I might have a more positive attitude and I did
get 160 hours out of it, but it seemed a bit cheap of them.
On the other hand, they did tweak the engine somewhat: FO3 had some very nasty game-corrupting bugs that seem to have gone away and in my experience NV ran a lot more smoothly, unlike the judder-fest that went before. But I'd say it was more of an albeit big expansion to FO3 rather than a fully-fledged game in itself.