For example, I'm a bit of a Browncoat - I used to be obsessed with the TV show Firefly. I was one of those people struggling to try and get it back on the air after Fox cancelled it. Nowadays I've sort of come to terms with it, though. They wouldn't be able to put together another season, even if they brought back all of the original cast. That show was one of those rare occasions where everything just came together in just the right way; and you simply can't recreate something like that on purpose. Another season would likely pale in comparison to the first one - you simply can't live up to yourself in situations like that. The moment's passed, and it's highly unlikely you'd be able to get back to the same set of circumstances. And that struggle would probably show in the end result - people would be trying too hard (or not hard enough) to recreate something that had once come together naturally.
Just look at all the times actors have tried to spin themselves off after their show has gone off the air. I actually became a bit of a fan of Friends, for example. I thought it was a pretty funny show, and Joey always cracked me up. But then when he tried to do his own show based just off of his character, it didn't work. The chemistry just wasn't there.
I have my gripes about Fallout 3 based on it's own merits (just as it's own game, there are things that I don't like about it so much.) But I feel it's also about as "Fallout" a game as anyone was ever going to make. It never really had a chance of bringing me back in time to nearly a decade ago, and making me feel the same things the first one did. That was simply never going to happen in the first place.