The soundtrack and universe are great. I've always been interested in exploring Granblue's world, and I'm finally done. I still see that it can improve in the future, but for now it completely SUCKS. It's shit.
I don't care about gameplay so all I'm left with is the story, which is ridiculous and poorly done. Anyways, Granblue is a massive series with an expansive worldbuilding, as there is much yet to show, it's unfair to judge the series as a whole for now.
But, yeah, having waited years and years for this game and having it be a disappointing experience, it was sad.