Fallout 4 is a good, generic open world RPG. It is a terrible Fallout game.
Because I know it will be asked, what makes a Fallout game a Fallout game that Fallout 4 failed at?
In fallout games, you are an active participant in many stories. You make branching choices in those stories. IE: Quests can be solved in multiple ways.
In Fallout 4, mostly, you only have a binary choice. Do whatever quest or do NOT do whatever quest. There is very little, “on the how” you chose to solve a quest and even when there is, it makes very little to no impact upon the world.
Also the wold is mostly populated by generic bandits / mutants. The only story you get involved with is reading it on a terminal opposed to a typical fallout game where you live the stories and make moral choices.
Of the endings of fallout 4, 3 are almost the same. 3 of them give you a new radioactive crater in Boston. How that is accomplished is also almost identical with just a different aesthetic on NPCs doing the dirty work.
3 of the ends also end up with the prydwen blowing up, again with the only difference is the detail of how that is done.
In the end, the wasteland doesn’t change with the possible exceptions of a new radio active crater and/or smoking remains of an air ship.
You do not have any real say in how any quest line turns out. You only have the choice of doing the quest line or not doing the quest line. The “how” and its impact is almost completely missing from fallout 4, which is why its not a real fallout game, IMHO.