Well, I guess the biggest draw is the world building. This is a continent with different nations, all with a detailed history and different cultures, etc. This series focuses on perhaps the biggest and most powerful nation in that continent, Erebonia. Trails in the Sky takes place in Liberl (a different nation that borders Erebonia) and the Crossbell series takes place in, of course, Crossbell, another neighbour of Erebonia.
In a continent like that, there’s lots of space for potential and actual conflicts and tensions, which feature prominently in the storytelling of all the subseries. And there’s also remains of an ancient civilization in the whole continent, and all sorts of legends connected to that. There’s also a secret society wreaking havoc everywhere, as part of a larger, mysterious plan… so, there’s a LOT.
Anyway, it’s a very nice backdrop to tell a lot of interesting stories. And the games do that by focusing on characters, in how they connect with other characters, and what effects the many events that take place have on those characters. It is at once grand and small, with that kind of focus.
Gameplay-wise: being a character-focused game with lots of storytelling, you talk to a lot of people and go to a lot of places to talk with a lot more people. There’s some exploration, but it’s mostly linear and focused on a chain of events that slowly unravel even bigger plots and mysteries. It is a slow burn because of that, which explains some of the many hundred hours in the series, because as a game it takes time establishing the setting, characters, motivations, etc.
As for combat, it’s really good. Turn-based, of course, but there’s a lot going on. Each character has different special attacks and all have their specific strengths and weaknesses, there’s a fully customizable “spell” system, and you can manipulate initiative to delay enemies or allies to better use the random effects that can happen in certain turns (like guaranteeing criticals, recharging your spell points, and lots of other stuff). As you unlock more options (and sometimes the ability to choose your party members) it gets a lot deeper than it looks at first.
So yeah, that’s it? I love the combat, I really like the detailed world they built here, I like the characters, and the story is pretty interesting and goes to interesting places. That said, the game takes its time setting up everything, so anyone with little patience for “slow” games should probably stay away.