After playing FO4 for about 25 hours over the last month and about 10 hours of FO76, I'm really starting to think 76 is by far the best Fallout experience Bethesda has ever developed directly.
It takes everything the fourth game did well and just improves upon it, ESPECIALLY the writing and RPG systems; to the point where it kinda ends up being their best single player Fallout game despite essentially being built as an MMO. The conversations are more interesting, the quests take you to cooler places and oddly enough it gives you more freedom when interacting with NPCs than the fourth game ever did (at least in my somewhat limited experience so far).
The map is also just incredible and I've barely seen like 20% of it if even that, but even stuff like interiors feel so much more interesting than previous games overall (if you've seen a Super Mutant or Raider camp in FO4 with their bags of meat everywhere you've kind of seen them all). I was beginning to sour on FO4 thanks to (among other things) the settlement stuff, and that whole aspect also seems better implemented (and more avoidable) here.
New Vegas is still untouchable and the best 3D Fallout game by far, but I'm pretty pumped that Bethesda managed to create a truly well-realized version of their own interpretation of Fallout. It feels like a real, involved (yet managable) open world survival exploration experience instead of a huge theme park using iconography from the previous games without much rhyme or reason (which was also fun in its way, but I prefer how they're doing their own thing with the creatures and design of 76).