I don't agree that the player should never have spare time. However, most of time, they shouldn't.

In Fallout 1, the vault dweller didn't have time to sit around and decorate his house because he had to find the water chip or the vault would run out of water.

In Fallout 2, the chosen one had to find a GECK or his people would all die.

In Fallout 3 and New Vegas the MQ isn't as urgent until you actually get further into the game so I could kind of see it working there until a point (Vault 87, House Always Wins)

Lore.

Let's face it; most games can handle shifts to just about every aspect except some core points of lore.

Doom wouldn't be Doom if it didn't feature an invasion of Techno-Demons.

The Legacy of Kain series is nothing without Nosgoth.

Neverwinter Nights isn't the same if it leaves the Forgotten Realms setting.

Fallout wouldn't be the same if it didn't deal with... well, the Fallout of a nuclear war.

For me it's the Lore. As a History Major, one of the things I bs a lot with classmates and friends is alternate history, so a divergence from WWII is intriguing. That pre-war civilization clung to a variant 1950s as a warped nostalgia for so long, I find fascinating. Seeing how the tech developed with those points in mind is interesting. A good chunk of my playthroughs in FO3 and NV were just exploring around seeing what I could see since my playthroughs of Fallout 1 & 2 were mostly "OMG I'm not going to achieve the game goal in time!!"

With that said, I'd also like to see some rebuilding/advancement from what we've seen in the game so far such as would we start seeing things like a retro 60s or 70s developing. But then I wouldn't mind running around the wastelands in go-go boots, a minidress with a minigun and a beehive hairdo.