The kiseki series is very unique in that all of its games have direct continuity. 8 games in, CS3 is the first game that really takes advantage of this in terms of regularly calling back on previous arcs.
I'd say all of CS3's best moments come directly from it taking advantage of the legwork of older games. Chapter 2's entire Crossbell segment comes to mind first as the peak of the game, as does Chapter 1's ending in Hamel, the appearances of several old party members such as Randy, Tita, Olivier, and so on. I could see some getting upset at the game's peaks all being built atop games that were written over a decade ago, but given the uniqueness of the series, I'm willing to let it slide.
CS3 also does plenty of its own work. It returns back to Zero's style of favoring smaller parties and only occasionally introducing guests, which does wonders for the characterization of New Class VII. I like every party member in NC7 more than most of CS1 and 2's main cast. Special mentions go to Juna for managing to be an incredibly likeable and interesting character in a series where the party members often have secret identities, tragic backstories, and/or preexisting connections with major NPCs.
One interesting thing is that CS3 doesn't really have much of a plot. In terms of accomplishing a goal or causing change, basically nothing happens before late Chapter 4. I will admit that the lack of agency bothers me sometimes, but overall they still manage to make the game interesting through worldbuilding, political intrigue, and the character interactions, which is impressive.
The game's combat is also probably my favorite in the series so far. Now, there's a big asterisk on that statement, because I played on Nightmare. If you go any easier than that the game collapses in on itself with how many different ways you can snap the combat in half. However, if you play on Nightmare, it feels like the combat was designed with that in mind. The broken strats are the only way to survive, and you will not achieve them quite as easily as you might hope. Even in the endgame where I have amazing equipment, quartz, and all party members, I'm still sometimes struggling to stay afloat in the boss fights. The combat is almost always engaging and fun, which is honestly a rarity in this series. I feel saddened that Steam's achievement stats told me that less than 10% of players got to experience this game's combat at its best.
My only real issue with this game is the fanservice. It is fucking ridiculous, especially at the start. The game rapidly alternates between having incredibly cool moments and having shit that makes me want to turn the game off. Most glaring examples are the actual rape scene between Shirley in Duvalie in chapter 1, and the entire existence of Musse. Personally if I were writing a game where the protagonist was a teacher and had multiple party members as his students, I'd have veered away from the romance aspects, but I suppose Falcom had other ideas and wanted to make sure everyone knew it. Everything else is great. The rampant fanservice is the only reason this isn't a 10.