You're not alone. I'm in the same spot. I love the humor of Fallout and I really liked the TV series; I have played Morrowind, Oblivion, more Skyrim playthroughs than I can remember but I bounced off FO3 pretty hard. For me it was the dreary environment and overall decay of the world.
People in FO3 just didn't seem to care much about their living conditions and this doesn't seem like what would happen in actual post-collapse society. People in general love surrounding themselves with art and beauty, rusty scrap metal shacks wouldn't be around two centuries after the bombs drop. Earthship, stucco and clay bricks are low tech but can be made very pretty and livable. Murals and paintings made using various pigments, colorful textiles, basreliefs, carvings and sculptures of ceramic, wood and stone would be everywhere, sprinkled with surviving pre-war artifacts that's been restored, maintained and cherished with pride.
Plant life would also recover quite fast and be lush in a post-atomic war world—Chornobyl is a prime example how nature claims back human-abandoned land just decades after a nuclear event. Deserts in FO should not be all dreary brown misery; there would be a thriving ecosystem of both flora and fauna. Two centuries is enough time for the most dangerous radioisotopes to decay away and you wouldn't really find places where radiation would stop wildlife reclaiming the land. More mutations and birth defects, yes, but life will find a way.
And this overall miserable representation of post-apocalyptic world is the reason FO games never really clicked for me even though the satire and tone hit the spot.