Truthfully I've only played Oblivion and I can clearly see the similarities between that game and Fallout 3. What Bethesda essentially did was take some of the plot devices and interesting factions from the previous Fallout's and combined them with Oblivion's mechanics and put a post(barely)-apocalyptic coat of paint over all of it. Fallout 3 is, essentially, a hiking simulator, its primary focus being in the exploration. This is what Oblivion was about, but it was never what Fallout was about.
I'll put it this way- Bethesda is a lot more, and deeply, Ultima inspired than Cain, Taylor, and Anderson were.
Ultimately yes that's a large paradigme for BGS but as Oblivion's the first work you played then the close coming of FO3 your missing out on the fact that it's the lifeblood BGS has run on since 94'. The alienation of Oblivion largely was the weak writing due both to BGS not being the best writers and full voiced game for the first time in the main series, and the standard fantasy vision for Cyrodiil.
Or it could be the exploration, but again from Arena it's always been about exploration in a 3D world from a 1st person perspective, albeit not focused on you til Daggerfall.
What I'm trying to reach at is while FO1 is from first glance a whole different beast, not quite so at a closer look. Not to suggest FO3 is anything satisfactory, -As a Fallout fan.-
I don't want to undermine them or praise them to the heavens. Especially with the long time fans like me crowd I like to instill that Bethesda has key strengths and key weaknesses like all studios.
Now obviously even if something like had Van Buren happened I'd still be bitter and claim FO1 as tops. I'm a hard really devoted fan as well. I partly hate Avellone and Co. At release I threw my copy of 2 away.
FO3 is a distinct shift and 4 will continue that. I'm not going to pin BGS games as crap though. To each their own.
As to the development process, I lay part of the blame on Mr. Dark Brotherhood Emil. Half the things we don't like is due to his need for badassery.