I've been considering a question similar to this for the past few weeks, and, someday, I may decide to finally post my completed meditations on the subject. However, until that time, I'll simply remark that the open world, while quite impressive and beautiful as an environment in which to pursue adventures, does not, by virtue of its vastness, provide an environment conducive to the forging of a strong, solid, narrative chain. If we liken the quests in this game to the links of a chain, a strong narrative would contain many tightly-bonded rings, each one interlocking with the other. The result would be a story with the strength and tension to pull great weight over a long distance, with the structure for a heavy, and striking climax at its end. However, with the free-roaming exploration, unrelated quests, and potentially random order of events, most links of The Witcher III are only loosely bound, incompletely closed, and thus are easily detached by a stout yank, or a good shake. Some links remain isolated from the main line, and lie scattered about, unconnected, and unused.
The creation of this game was a remarkably ambitious undertaking for CD Projekt RED, and they are to be commended for their valiant efforts in attempting to realise this spectacular vision on so grand a scale. However, the appeal of this series, as we've observed, has never lain in free-wandering adventures, but rather in strong story-telling, with memorable characters, and meaningful decisions. This game was fashioned from a rich lore, and was preceded by two titles with firm narrative chains, where the world was made to suit the action, rather than the action made to suit the world. The story, its intricacies, characters, choices, and consequences were the virtues which attracted many people to the games, and earned CD Projekt an often fiercely loyal following. As a result of their ambitious aspirations, however, we've seen their admirers rage, complain, bewail, and despair in disappointment at the incompleteness of The Wild Hunt's overarching story, and unfulfilling ending. What should have been the driving force of all adventures, became a collection of scattered links, a broken chain, which, while sound in some places, was not strong enough to pull the weight of the world.