How about comparing metacritic scores?

https://www.metacritic.com/game/pc/fallout-3

https://www.metacritic.com/game/pc/fallout-4

One might slice and dice this by platform, but I think there was a general consensus that 4 was not as good as 3 both in meta score and user score.

Skyrim was a significant technical advancement of Gamebryo, not just in terms of visual quality or so forth, but also in terms of what was possible with the engine. Fallout 4 was a minor upgrade and could have easily been a total conversion mod for Skyrim - there was no innovation and it did nothing new. Irrespective of whether people enjoyed that re-skinned Skyrim, it was a blatant cash-grab.

The argument has nothing to do with anybody enjoying the game, a metric that I did not mention at all in my comment, it has to do with a growing trend where Bethesda has been doing the absolute bare minimum to cash in on their fans' good will.

It was a huge step down if you liked RPG games, which given Bethesda traditionally made rpg games and that fallout was originally an rpg series is hugely important.

Fallout 4 suffered from quest repetition/duplication, an emphasis on combat over other rpg driven approaches to play and a relatively low ability to effect the world as the player.

It's not a bad game per say but it's a mediocre rpg. It was arguably more disappointing given how incredible an rpg New Vegas was despite not having been finished properly.