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Bethesda create huge worlds, where every NPC has a unique character model, their own home, their own daily routines, all their equipment is lootable, every frickin' spoon in the game can be collected. No other game does that. The closest we have for an open world RPG is The Witcher 3 which regularly reuses character models, builds their clothing into the models, and doesn't have interactive clutter. Bethesda's engine focuses the hardware on scale and interactivity instead of on visuals. PC modders then utilize the engine's amazing mod-friendly potential to push it as far as they can with cutting edge hardware.
The unique character models is false, it reuses more than the Witcher 3, at least Skyrim that im playing now, and even like that, is an easier task when you have 4 NPCS in a small town and 20 in a big city total. The witcher 3 doesnt
regularly reuse characters models. You have to play like 20 hours to start seeing some kind of copypasting going. Thats an amazing job for a game that has like 50 different NPC's in the first small town and 1000 in a big city. In Skyrim you can find same face bandits 20 minutes into the game, and similar NPCs after you visit 10 habitable spaces (theres only like 10 different clothes for gods sake). All characters dont have a home either. The AI daily routine of Skyrim is basic at best, handling a very small number of of NPC's at any given time (you can see that when you pass time fast, npc's dont move from where they were if you are in that zone, while they do in The Witcher 3, and 1 and 2 IIRC).
The building the clothing into the models is also easy in Skyrim, because everyone and their mothers have the same bodybuild, something modders have had a hardtime to make it varied (most mods only choose to do the same, create a new body, but still for all characters, you need to find a harder to install model that tries to make variations).
I would really prefer if Bethesda build a big city in their RPGs(maybe not in Fallout, becuase of the total anihilation) with 500 people, and make 20 of them totally varied with their own problems and quests, than try to make every NPC in that "city" say something different but totally mediocre and just a few lines and a shitty go and feth me this quest.
I dont really give a fuck of graphics right now in Fallout 4. They are not pretty, but serviceable.
What im more afraid of is if they still dont know how to make interesting quests, and varied and charismatic characters. You dont really need an out of this world computer to make that, and is a thing they could change if they used the insane amounts of money they win to hire new and better writters and escenario directors.