So, I beat the game some weeks back. I bought it out of a morbid curiosity and hearing that it was a good JRPG and enjoyed it for the most part. The Fire Emblem tie-in was mostly lame; it didn't help that they just took characters from the Akaneia games, which aren't really where the best characters are, and barely developed them. Per the OP, I'm not allowed to talk about the idol thing, but that wasn't as obnoxious as I thought it'd be. But I went in knowing I'd have these complaints, and as I said the idol one wasn't as bad as I thought it'd be.
So some thoughts:
I liked the battle system a lot, particularly early on when you don't have as many session skills and have to think a bit how to best use your turns and subcast to get the most out of combos. That strategy disappears mostly by the end when your session skills are maxed out and everyone can attack from the subcast. I immediately started over on lunatic just to experience some of the early battles again; got through chapter 1 again before I moved on.
The dungeons were generally neat, but I think their stories were going for the 'dark side' of idol life while the main cast always turned the story into the boppy side of idol life, which made it seem like they didn't get what was going on at all. Still, I enjoyed the light puzzles, bosses, etc.
Chapters 5 and 6 were weaker than the earlier chapters. 6 was fine from a dungeon standpoint, whereas 5 was retreading (although thankfully with expanded puzzles). 6, however, was the triumph of the lackluster Fire Emblem underbelly in terms of story.
The sidequests...are of varying quality, with some of them seeming undercooked and others pulling off a degree of 'anime' charm without having anything deeper going on. Basically contemporary Fire Emblem support conversations, I guess. Having since gone on to play Persona 4 (bought that and Nocturne after playing this), this looks worse in hindsight.
As to the requests, I felt I never really got anything for doing them. Money and items were never a problem and the locktouch is the only one I remember, which I thought was something cool to get. More player abilities should be tied to them or something.
As to the characters...well, per the sidequest statement above, I think pretty much all of them, except for Tsubasa who got a lot of service in the early parts of the main story, were undercooked.
The harem game made me uncomfortable. The game was simultaneously pushing hard a 'canon' Itsuki/Tsubasa relationship while also have every female in the central cast want in your pants. For me, Tsubasa was on that side of anime cute where it is always a mix between adorable/amusing and disgusting so I didn't find her particularly attractive in that way. At the same time, none of the other options were developed past people hitting on you and having random crushes on you. Moreover, other than using salacious dialogue, I guess, (which I wouldn't do in real life or in game
) you couldn't make a choice in game. Basically, I liked Kiria the best from a personality/looks perspective but I found her sidequests and romance 'angle' lacking, while I also found it pretty awkward/awful to do Tsubasa like that...