Its ending gives much better closure to the whole game, and leaves the players with a greater sense of achievement. That is, unless one pursues the main plot relentlessly without random exploration at all, which defeats the purpose of CRPG's in the first place. To put it simply, suspension of disbelief is easier to achieve and keep with Fallout 2 . But one cannot ignore the fact that Might and Magic 6 has a certain appeal by being as big and open- ended as it is. You can do whatever you want.
Freedom of choice has a value in itself, especially for the serious role player.
Even if there has to be a central plot, the better Dungeon Master will always know how to cope with the most bizarre and unexpected of his players' actions. Fallout 2 simple does not allow one to do much in the way of unexpected actions. You cannot join the Enclave, for example, or kill all the villagers. You cannot, looking deeper into the game, be the bad guy. You will always have to fight the new US at the end if you want to finish the game, in essence playing out the heroic role of the savior.