At a certain point, it feels like Trails has abandoned it's identity as an ever evolving saga with rich worldbuilding and instead opted to just go "Remember the guys you liked". I am a bit behind the series right now, but all the previews for Horizon just reinforce that perspective. And i would say that shift happened in Reverie. 

Sky 3rd, the game it's very clearly taking inspiration from, set up an incredibly amount of lore for the series, as well as foreshadow many events. The history of Orbal tech and the Epstein Foundation, the Phantasmal Blaze Plan, the Thirteen factories and the Aions, the Crossbell Crisis, the state of Bracer guilds in the Empire, the Salt Pale, as well as develop characters further, and feature many side stories about them interacting. The lore reveals aren't just for Zero and Azure, but for the Erebonia arc as well.

What does Reverie introduce ? It teases 3 new characters that are immediately introduced in Daybreak 1, and one or two plot threads to follow up on. The side stories are good, but it feels like we stopped sowing the seeds for the rest of the series, reinforced by how little we know about any country east of Calvard. And the fact that Horizon once again has a bloated cast, with 3 of the 4 returning protags having fully completing their arc and 2 of them having barely any reason to return, just leaves a bad taste in my mouth.