I would go the MW/FO3 approach, which would be to make every dungeon special, every dungeon would have something that would set it apart from the others.
With the outside landscape, I'd have a land of extremes, like MW. Mountains going up to the very heavens themselves, that new players wouldn't suspect you could go past. As the game progresses, you get to see that, indeed, there are lands beyond these massive peaks. Past them you could see all sorts of different places. A land of opposites, that's both unforgiving and exotic.
Also, gigantic monsters. Seriously, gimme a fourteen foot tall mountain troll to wale on or something, for once. FO3 knew how it was done with the supermutant behemoth. God, were those ever fun.
It'd also be nice if sometimes you would just fine an army of little ankle-biters in some dungeon, and you could just fight off wave after wave. Of course, their bodies would disintegrate after some time, too, or else the game would crash sooner or later. Again, dichotomy is important in varying the environment. It'd make you feel accomplished if you could kill endless hordes of little monsters, and it'd make you feel like a full-fledged hero if you also went up against that same ankle-biting army, with some gigantic enemies thrown in.
So, how would YOU make TESV more epic and sweeping, without making it take up four discs or something?