I wouldn't mind Obsidian making a stand alone product like New Vegas once Bethesda is done making DLCs/expansions. I'm pretty sure Bethesda gave them a design document for new vegas because the quality it had was insanely better than the DLCs. Vegas itself was better than fallout I thought. It was great. But that DLC for vegas I played felt worse than SHivering Isles for Oblivion by a long shot, and way worse than the fallout DLCs. I'd say Obsidian designed it, as it svcked ass.
So whatever they do, make sure it's good this time, I don't care who makes it, as long as Bethesda does the design document. Make it big and bold, not some cheap add on is all.
Many fans it seems are divided in their feelings about that particular dlc. I remember my first time going through, wondering when it would be over, however on subsequent playthroughs, and paying more attention to its theme and story, I began to appreciate it a bit more.
Dead Money was never supposed to be a sandbox of any sort. The point of it I believe was to tell the story of the Sierra Madre, and to instill the fact that the place...despite whatever promises and treasures it once held, had been warped into "a special kind of hell" giving off a sense of dread and hopelessness, a place that is completely hostile....transformed and destroyed even before the bombs fell. Made only worse with time.
The real main character of that dlc if any..in my opinion was the dead starlet Vera, the casino itself, and the theme of "letting go". It's a posthumous thing, the actions and lives of people long dead...still influencing or otherwise marring the present.