And yet, almost anyone talking about Fallout today is talking about the franchise from Fallout 3 onward, so... Fallout 3 is Fallout, regardless of internet navel-gazing.
Franchises should (I think) evolve. Hopefully it's good for them. Sometimes it's not.
Honestly, there's just a fundamental divide which means this will just be an endlessly looping discussion until everyone loses interest.
On the one side, you have people who view mechanical decisions as franchise-defining (mechanics-first). Is Fallout an isometric rpg with turn-based combat or a first-person rpg with real-time combat?
On the other, you have people who view themes, narrative, and general design choices as franchise-defining (framework-first). Is Fallout about a vault-dweller navigating the wasteland, making (hopefully) meaningful choices and telling the resulting story?
I find the mechanics-first approach to be arbitrarily limiting to a franchise's potential, ultimately resulting in tired retreads of the "same old thing" over and over again. The framework-first approach, in my opinion, allows for mechanical innovation and fresh ideas. It might not always work, but ultimately I still find it a more appealing approach.