Y'know, they could probably actually get the "big" world map feature back using their fast travel system, but frankly, after having been playing it again, the ceaseless wandering around was pr. atmostpheric and depressing, aside from the nigh-constant random encounters. Basically you'd pull up your pip boy map, you'd get multiple levels of it, starting out wide (eg, Capital Wasteland, The Commonwealth, etc). You'd pick a spot like the Capital Wasteland, and you'd get your little marker to travel, random (interesting, hopefully) encounters could pop up, and then you'd get there, and you'd have a bigger, open area with multiple towns/settlements etc to go through. You'd retain the level of wasteland exploration that FO3 had, but still be able to scale it out wide, and give the implication that the centers of humanity are concentrated.
Or, for the older games, You'd set course for, say, NCR, and when you got to one of the surrounding squares, you'd go to a closer in view, like normal gameplay. (But still imagine this from the first person perspective), maybe you could find little shelters, or landmark type things (where quests could take you, random encounters could happen, etc) and NCR would be out there in the distance. If you were lazy you could use a more local Fast Travel system to get over there, or you could walk and eat up the atmosphere.
I'm kind of rambling, but if that makes any sense to someone, tell me, because I think it's brilliant.