Previous mods allowed players to continue with other side quests and activities after the conclusion. New Vegas, revered by the Fallout cognoscenti, now has a proper end-game mod, in which the world goes on after the all-out fight at Hoover Dam. Either outcome sent me the clear message that New Vegas’ best feature, the sprawling, wide-open land of choice and opportunity for my Courier, had narrowed considerably, and things were now speeding toward a true end - as in, no more playing, not just the conclusion of the story. House or wiping out the Brotherhood of Steel on his orders.
Hell, for me it actually came well before that point, whether it was killing Mr. Having finished Fallout: New Vegas twice, I can attest to the bereft feeling that comes after completing its excellent main story arc.