Dungeons, instances, ruins, indoor places of exploration in independent cells. FO3 had plenty of these not related to any quests. Bethesda Offices comes to mind. As well as the Dunwich Building and even an armory or two (they even had decent loot). Where's the Wheaton Armory of New Vegas? Where's the Keller Family Transcripts of New Vegas? (I don't consider the Star bottle caps to be the equivelant. Pew pew versus the MIRV)
2. Random Encounters
You never quite knew what was gonna happen over the next hill or down in that ridge there. A wandering merchant? Two wastelanders arguing over how to dismantle a frag mine and blowing themselves up? 3 captives guarded by Super Mutants? It made the Capitol Wasteland a tad more exciting.
I'm probably already beating on an old dead horse by this point, but I felt I had to say it anyway.
