We could compare it to its contemporaries, like Starcraft or Diablo, both of which sold millions of copies. By any stretch of the imagnation, the games were duds.
You're comparing games that were designed for mass market appeal with games targeted at a smaller niche. As I said, not every game has to be a mass-market AAA title, nor every game should.
FO 1 and 2 were huge, streaming piles of [censored], with a ridiculous combat system - when a contemporary game like Diablo managed a much more dynamic and intuitive system that becamse the standard until 1st/3rd person took over - and a long and convoluted plot with lots of potential outcomes, assuming you weren't so bored you gave up and used the CD as a coaster.
So, you're simply not the target audience of the Fallout games. Now tell me, why should a sequel to Fallout be made to appeal to people who hated the originals? Wouldn't it be better if Bethesda simply created a new post-apocalyptic franchise? It's not as if people who don't like or didn't play FO1 and 2 would care.