I can't believe that some people didn't enjoy exploring in NV as much as FO3. I'm the polar opposite. Exploring in FO3 svcked. I hated subway tunnels, by the end of that game. Seemed like you couldn't get very far before having to take one. I'd totally be up for an Obisidian TES, unless Bethesda changes the direction they're heading.
Exploring in FO3.... wander around, find an unmarked/no-map-marker building, go inside and find bunches of rooms with a funny/sad/interesting/whatever story told through debris arrangements and terminal text.
In FO:NV.... wander around, find an unmarked building, go inside and find a lobby and two collapsed hallways leading from it. Nearly everything that wasn't associated with some quest ended up being 2 rooms and a pile of nothing. Even some of the quest locations were pretty small.
Yes, NV's world made more "sense". (FO3 has so many logical inconsistancies, like how do all those people survive in their little enclaves, how do the raiders manage to keep going as cannibal psycopaths living in a pile of rotting guts, why has no-one swept the floor in 200 years), but the locations themselves were vastly more interesting than the ones in the Mojave.
And, honestly? Beyond the first playthrough (where I follow the plot), additional plays of Beth games, for me, are frequently just wandering around the map finding the nifty stuff that's hidden in corners. Stuff like the sewer near the Capitol where the guy tried to jump his motorcycle over a car. Told entirely in debris. Or any of the million other things you can find in FO3. (Grrr..... still trying to get that damn program to work with Win7. Haven't played it in way too long. And I'd love to see it on my better system.)