I have mixed feelings about the Shadowbringer storyline. On one hand, it's really interesting for the greater overarching story, it tells us more about the calamities, about splitting the world, Zodiark, Haydelyn (or however she is written) and last but not least the Ascians, who they are and why they do what they do.
But taken for itself, i think the story is pretty boring. The problem is that there are no turns, everything is extremely predictable, and basically always the same. You just go from area to area and kill one light warden after the other, there is no change, nothing happening that forces you to put down what you are doing to solve another pressing issue that requires some time to solve. The other few issues that do come up, are solved really quickly, so you don't get any break from the light warden hunt. And after achieving your goal of killing the light wardens, there is only one other thing to solve, but that was talked about for the past 3 areas, so it doesn't feel like a change of pace either. And honestly, i didn't care enough about the Crystal Exarch to be really distressed by his kidnapping. Even the NPCs were talking about it only as a side note, saving the hero was much much more important for them.

My feeling is that the story of Shadowbringer is basically the setup for the next expansion where we will bring it all to an end. So my guess is the next expansion will be the last one, just from how the story flows. Or it will start a completely different saga, one that isn't about the Ascians anymore. Kinda like Avengers Endgame was the end of an era in the MCU and the overall story will move to new, unfamiliar fields.