It doesn't, actually. Fallout's following is hugely built on north american videogame news websites not understanding what an RPG is and calling it "the best of the best" because it has guns, dialogue choices that seem to make any difference whatsoever (they don't, really) and an open world -- those are the three best elements for your game to sell in western markets.
Half the people who ever (over)rate Fallout 3 and New Vegas, as well as the same people who are now overhyping the living hell out FFXIV Gil of Fallout 4, admitedly never even played the first two. Just to make it clear, whatever "acclaim" the series had -- whatever elements made that happen -- are both long gone, and pertain to chapters 1 and 2, *not* 3, NV and most certainly not 4 by everything we've seen thus far.
This is not even taking into account the massive dip in quality from Fallout 2 to Fallout 3, whose successor (as well as itself) became little else beyond a glorified shooter with a level-up system. Fallout 4 already has been confirmed to strip down even more RPG qualities and retaining only the most basic and "marketable" elements such as yet another half-empty open world and dialogue choices. In fact, this is so much the irony of the situation, that even the dialogue choices have been reduced from the first ones, where even small player-related things such as your character's intelligence stat would have a direct impact on what choices he or she could even make. And I'm not talking about greyed out dialogue options. Buy FFXIV Gil I'm talking about dialogue options created *specifically* for dumb characters and intellectually brilliant characters, which didn't exist unless you were one or the other for obvious reasons.
Stats. Remember when that made a difference?
At the end of the day, you play whatever you find is the best for you; I'm not trying to judge you on that. I don't exactly agree with the way Yoszen put it, but the jist of what he said still holds true. Sorry.
Enjoy Fallout 4.