Bear with me here, but there are actually some people who say Fallout 4 didn't, at all, try to rip-off the plot of New Vegas. Let me go over several plot points.
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You, the main character, had something done to you by a guy with a deep, complex history who had plenty of experience with the land you were about to find yourself in.
You leave the area of a lone settlement in the middle of nowhere, while trying to track down this one guy with the help by directions given by the people you meet in several settlements along the way.
The search leads you to the big city and the central settlement of the entire wasteland you are in.
Eventually, you find who you're looking for, and the guy has apparently been screwed over by the one of the major factions that plays the "antagonist" role.
After dealing with him, you're offered (well, more like pressured) to work with this antagonist faction in deciding the fate of the wasteland.
You work with your choice of four different factions:
- one that holds the most pure military strength in all of the four, whose leadership has several flaws and who many in-game civilians do not trust while many real-life players think are awesome;
- one that represents your own leadership and decisions and is an independent standing force ordered around by no one;
- one whose leadership have their own agendas and are using you for their gains while preferring tactics of using deception and subterfuge to gain a technlogical advantage,
- and finally, the "villainous" one who possess a much more complex mission and history than the entire game has made you think.
The ending is most different if you decide to work with that last one.
The original reason you set out for has its meaning lost, as you're pulled into a web of bureaucracy and war to determine the fate of the wasteland, at which point you're forced to take out other factions you've probably been working with before.
The final battle all takes place in the same manner, save for the "antagonist" faction's one.
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For fuck's sake, they would've done better just remaking New Vegas in the Creation engine.