What people fail to realise, is that New Vegas was (supposedly) buggy for two reasons: one, it used an outdated engine that was already pretty damn buggy, and two, Bethesda really dropped the ball when it came to the deadline (let them delay it longer, if it means more testing!)
So now that that's out of the way, I think there would have been fewer followers, but they would have been much, much more memorable, and I feel there'd be harder choices to make when it came to things like the Dark Brotherhood ("No, I'm not killing that 'guy on the boat', thank you very much!" for example).
However, while Obsidian is better at writing, they're worse at level/world map design.
So uh, yeah Bethesda + Obsidian together would be a pretty legit alliance. Agree?
Fallout New Vegas was so linear it was ridiculous. It was cleverly disguised, but linear nonetheless. You left the vault, then what choice did you have. End that cute little fued going on in town. Then what's next? Head in a predetermined path to New Vegas, doing the exact same quests the entire way. Then this is where you get some imitation of choice. Bad guys or Good guys? Doesnt matter. You are still doing the same exact quests in the end. And guess what you got when you wanted to start over? The same thing over again. I never ever like the earlier game in the series. For me, its an unheard of trait, but Fallout is the only game where I like the original Fallout 3 more. So if obsidion made it instead of the Gods among men we call Bethesda, we would have got iron sites on our bows, and we would get cut down by death claws if we decided we wanted to go to solitude first instead of retrieving the Claw. Beth knows what the hell they are doing with the elders scrolls, and they have been with the series since it was a wee lil' Daggerfall, and i would trust no other mortal with the design of The Elders Scrolls.
You were never in a vault.