I have to agree, Bethesda's Fallout 3 was so lackluster from the RPG prospective I almost didn't bother with New Vegas. And after Fallout 4 I certainly won't bother with Bethesda's Fallout 5 unless they make a 180 degree turn around which I really don't expect.
I had so hoped Fallout 4 would be that 180 degree turn :cries: There was this one interview after Skyrim where Todd Howard said they are now really good creating interactive worlds and they're now going to focus on characters and story. And I was like 'OMG YES!'. Shortly before the release of Fallout 4 he mentioned that pacifist runs are no priority for them (which sucks given the legacy of Fallout 1, 2 and New Vegas) and well, then came the release and we all know how that turned out
I don't think I'll hate Fallout 4 - but they really really went in the opposite direction of what I had hoped Maybe there's hope for a new Obsidian Fallout - maybe...
To get back on topic: The more I think about it the more I tend towards main story. Open worlds can be great when the story, characters and locations really create a dense and interesting place. I think that probably only works for smaller worlds - the bigger it gets the harder it is to fill the world with life. I'd be really happy with a medium or even small sized open world as long as it's well tied in with the story. There has to be a lot going on - and not just this one time the player is doing the quests in the area. Because that results in a world that feels depressingly empty once you return to any area that you have already "cleared".