The only people who like Fallout 3 played it when they were 12 and didn't know any better. Hence zoomers and young millennials on Reddit think it's a classic, and gen xers and old millennials on the Codex think it's garbage.
Kind of funny how every generation's favorite games are the ones they grew up with.
I'm born in 92. I'm probably the direct demographic oblivion targeted(within 2-3 years each way) and I thought it (and morrowind before it) were complete garbage.
Growing up Fallout 1-2 were my favorite games(my dad played them which is how I got into them) but for me they also stood out from other 90s/early 00's rpgs I played. I was too young and never played any ultima/wizardry(except 8 very briefly) and gold box games.
Fallout 3 to me, even if it didn't have the fallout name and butcher the lore/universe would have always been garbage. It's literally oblivion with guns and both end with basically a pokemon battle the player has no agency in.
Fallout 3 and Oblivion/skyrim obviously have a certain GTA style appeal. You walk around a mostly open world and do whatever you want in whatever order you want barring the main story. The characters are mostly silly and light hearted. The games are extremely easy with essentially zero challenge. Walk around do busy work kill shit. There's a fairly large demographic that wants nothing more then that from games. I have a friend I've known since highschool who basically only plays newer bethesda games(oblivion onward), GTA and online fps. He's a smart guy but when he plays games he plays them to turn his brain off and just walk around killing shit.
To me Oblivion and Fallout 3, even if they aren't the worst games in a vacuum. Probably represent the greatest decline in generational intuitiveness and intelligence. I say this as a 90s millennial but I never understood the appeal of playing games with the intention of shutting your brain off(anyone who says they need to use their brain for these games probably doesn't have much to begin with). Player agency and player choice(both in story and methods to complete objectives) always mattered to me more then anything else.
Over the years I haven't been that active on this site, but from what I understand this site was essentially built on shitting on Neverwinter Nights and Morrowind. Obviously people, opinions, demographics change but whenever I see someone saying they enjoy Fallout 3 or Skyrim or Dragon age or whatever other garbage the AAA rpg market spit out since the early 00's, I always think they took a wrong turn and ended up here by accident.