I voted original Fallout fans as the most satisfied and Fallout 3 generation as the least. I would hesitate to say Bethesda fans in general were disappointed, since it really depends on how many play these games for the roleplaying and lore versus the action and exploration. That group would also encompass fans of Daggerfall and Morrowind, and plenty of those people were disappointed in the streamlining and shift towards hack 'n slash that went on from Daggerfall through Oblivion and so would probably approve of the shift back toward RPG-mechanics. Fallout 3 by itself, though, has a gameplay style that vastly different from the original Fallouts, so it's not too difficult to imagine the reaction to a game that tries to appeal more to the original style when it's drawing in a crowd from Bethesda's rogue-like dungeon crawler.
I'd technically fall under the Fallout 3 generation / Bethesda fan since FO3 was my introduction to the franchise, but I still think that NV is superior to FO3 -- despite some glaring flaws (invisible walls, overabundance of quest items, etc.) and Obsidian's QA (or lack thereof).
While I loved and played the hell out of it, FO3 has IMO some of Bethesda's weakest world-building to date. As for the "zany" feel that Fallout 3 has and New Vegas supposedly lacks, it only really does so by having its "colorful" characters (Moira, Bittercup, Sierra, etc.) acting as if they were living in the Shivering Isles instead of a post-apocalyptic Washington D.C. Likewise, it achieves a more "depressing" atmosphere by removing all plausibility from the setting. Had this been set a few decades after the war and had removed all traces of the Enclave and Brotherhood of Steel, it'd be MUCH better. Then un-scavenged locations, people desperately clinging to old-world culture, still-working electronics, and fledgling settlements would make a ton more sense.
Bethesda's Fallout 3 should be re-titled "Fallout: D.C." and treated as a spinoff.
Wholeheartedly agree.