I think a big part of the problem is just hype cycles. People had expectations that were through the roof. They didn't tell you they had seamless transitions to space, and they didn't tell you they had BG3 caliber branching conversation trees (which we're a long way from being able to realistically do outside of a CRPG). But people seemingly expected that.
I watched the direct and we got basically what I expected (though the gunplay feels better than I expected. I definitely felt like VATS was needed in FO4.) It's Bethesda's game design philosophy of a massive world with a bunch of different play styles and a bunch of different quest lines (and smaller single quests) and locations that don't have to be done in any order. You can easily get sidetracked and go down rabbit holes. They iterated on most of their core features and adapted them to the new setting in a really well done way.
I also love the way the skill system brought back the "get better by doing" philosophy of Skyrim with challenges to unlock higher levels, and the story telling is sci fi in more than just skin.