Every saga has to end, for sure. The saga, as art form, is problematic, because the individual installment will often not convince as novels. That is especially true for thing like "the expanse" when the narrative sets out to follow a set of characters linearly over decades of in-story.

But we, the readers, have little right to complain: It is the sort of story we crave after all, because we crave a deep immersion into the narrative.

"Leviathan Falls" stays true to its predecessors: It shies away from potential narrative arks to focus on its characters and do them justice. Overall, that is the right decision.

The "closing of the gates" ending must have felt too defeatist to authors, so they added an epilogue where humanity is traveling between the stars again. It kind of works.

A decent ending which does not try to be more than just that.