For people claiming that 20-30 hours is not enough, you are demanding a lot of patience here when in reality, the amount of time needed to get in the game is an element of review (i.e. the pacing of the story/game needs work). A game shouldn't drag on with boring fetch quests to make itself seem longer. If that's the case (it seems like it is), then that is a valid complaint.
Most of these reviews are claiming that the story is not amazing like the original, and that many fetching quests exist. These seem like very solid complaints to me. Of course, there will be a few outliers that go "the graphix isnt ps4 good," but the majority seem to agree that the biggest issues lie in the story. And in an rpg, it would make sense to take down the game to the mid 80's as a result.
Overall I plan to get this game in the future, because there is more to a game then just a score. But I'm not going to go out of my way to give Xenoblade X a far better score than fallout 4 if the story and pacing is as big of an issue as people say