I'll bet my left nut that what players are detecting but struggling to express is a hasty implementation of a physically-based render pipeline that was merged into the engine mid-FO4 development. It results in subtle but discomforting aesthetic discrepancies where some textures look plasticky and fake because they don't reflect light the way our brain expects them to based on the visual information its getting from other objects in the scene.
The game's aesthetic is discomfiting and plastic but it goes beyond that. The whole world feels disjointed, the mechanics feel simultaneously cynical and half-baked (weapon mods and settlement building being in the game just because someone high up assumed it's what people wanted, as those features appear in mods/other popular games), and the quests are very low-effort with perfunctory stories (MW and especially Skyrim shared this problem but both made up for it with the quality of the worldspace in general). I've heard different people worked on different quests pretty much in isolation from each other, hence the wild variations in quality and tone. I'm not sure if this is how previous Bethesda games worked too, but I've always assumed - maybe wrongly - that Oblivion/Fo3 were written pretty much entirely by Emil.
It's hard to sort through all the reasons why this is the case, especially as I haven't tried playing the game again in at least half a decade, but I remember in the release thread, a number of us were all shocked at just how bored we were and how much the game was failing to engage us, moreso than any previous Bethesda game. Oblivion is the only game in the MW/Oblivion/Fo3/Skyrim era that I don't like and even that never felt as hollow as Fo4 does. Something had definitely shifted and it wasn't just the cruddy textures and lighting. The fact that I actually like Starfield shows that I've got a high tolerance for Bethesda shit but there's something very - again, for want of a better world - soulless about Fo4.
I suppose it's entirely credible that Bethesda fucked the game up all by themselves but I've always wondered if there was some kind of executive interference at work with some of the bad decisions made with Fo4, a suspicion which was bolstered after Avellone's story about how trying to contact Todd resulted in him being shuffled around various faceless managers who spoke for Todd without The Toddler himself ever being informed, though I think this story occurred somewhwere between Fo4 and Starfield.