IMO Fallout 3 only upset the Fallout fans, not the TES/Bethesda fans. It was too early, a new project for Bethesda and it did feel very much like Oblivion. It was much more like TES than Fallout 4 is, so many TES/Fallout 3 fans voted on Metacritic and with all the "efforts" of old Fallout fans, the score settled pretty high ( 8 - 8.5 ).
The trouble with Fallout 4 is it managed to upset people from both crowds, Fallout (old) fans and TES/Bethesda fans. A good portion of the negative reviews, if you take your time to read them, compare Fallout 4 to Fallout 3, not to the old ones.
So I think Fallout 4 objectively has a poorer reception than Fallout 3, there is no conspiracy going on. The critic score says the same.
Another thing to consider (by those who like the conspiracy theory that the Fallout 4 score was "bombed" with premeditation), is that we're talking about a mere 6423 user votes on pc, 3429 on ps4 and 1395 on xone. Supposing everyone voted for just one platform, we're looking at a mere 11.000 total votes, compared to 8-10-12? million copies sold. What I mean is this average score could very very easily be turned up side down if the pleased BGS fans who appreciate the game would bother to spend 1 minute to register on Metacritic and vote a 10 It would only take like 10.000 fans out of 10 million of satisfied customers. Why doesn't that happen? Maybe because the average is actually a fair representation of what those 10 million think about Fallout 4.