That might be true for fictional writing. Games are mostly about fun though.
^ A point of view usually shared by the Bethesda/Bioware crowd when facing criticism of these games.
I understand that you don't care about the setting or the themes that much, but you should be able to understand the nature of the criticism. For instance:
Furthermore, I do not see the need to let the player explore any theme to a major length and neither do you define in any exact way what exactly "exploring a theme" means in terms of thoroughness.
Many people do want to experience the game via exploring these themes because the first game did it so well. These people will be disappointed.
To me San Francisco is fine.
Because "games are mostly about fun though".
But what is Fallout 2's theme, anyway? I propose that the words of the game's intro have something to do with it:
But the scars left by the war have not yet healed. And the Earth has not forgotten.
I think the Enclave fits that rather well. The rest of the game, though, perhaps not as clearly.
I have two issues with the Enclave.
1) It's stupid. The idea that the government would retreat and wait out the devastation is great and logical, but it's been 160 years, which is a long time. They didn't evolve or change in any way. They still behave as it the war started 10-15 years ago. BoS evolved into a quasi-religious organization in 80 years with a clear goal in mind. The Enclave did nothing at all.
I mean, logically, you'd expect them to start taking charge after the war, re-establishing their control since they are clearly in a position to do so. Yet they sit and do nothing, frozen in time. That's why the fact that they don't play ANY role is jarring. Not because it's an enemy faction but because it's the US government with a fucking president.
Their attempt to go back to the old ways, to force the new powerful towns to accept their authority, their laws, pay taxes, etc would have fit the themes established by the first game perfectly. Not to mention, all 'philosophical' changes that would come with it. Unfortunately, they are just another theme park location, disconnected from the world, and existing only to show the player something cool and give him a tough endgame enemy to fight.
2) It's stupid. They want to release some gas and kill all impure humans, which is 95% of all humans, basically. First, it's dumb on so many levels it's not even funny. Second, it turns the game into 'save the world from retarded evil that would destroy it for the lulz', which is a pale and depth-less shadow of the Master's beliefs.