The San Diego Comic-Con has a dark side, certainly; a dark place, where fear is currency. Come to booth 1334 for succor.
By this point, you probably don't need me to tell you what Theatryhthm is. It's , or it's , right? Except when it isn't, exactly; except when it is hinting at an incredibly beautiful experience that it isn't yet, but could be. Korkomorka's Jason Schreier had an up detailing his craving for a true narrative RPG, gilded with these clever inputs.
There are RPGs that leverage rhythm as the primary mode of interaction, though, even if they don't bend toward the narrative end of the spectrum; every genre now steeps in powerful role-playing constructs. Rock Band is positively soaking in customization and progression. For the Patapon series, you barely need to make a case: these are Rhythm RPGs, full stop.
When it comes to what you might call a "full" JRPG type experience, the best example is probably Shadow Hearts. Don't be fooled by the shape of the Judgment Ring, a kind of customizable clock face which governs success or failure. It's all timing. And it does something very interesting, in that the attacks and abilities you choose alter the rhythms you must play. Different characters have their own "tempo" as a result; it's gripping. But Square places a lot of stock in its art, art you barely see in Theatrhythm because you're always looking at the notes. Gabriel loves this stuff, and wants to see it in a game where he can actually see it. But I agree with Jason that they should do this; I love spending other people's theoretical money on ultra high-concept plays. I also understand why they might not. But they've taken weird tacks with their flagship brand on more than one occasion; Crystal Chronicles leaps readily to mind.
The "endgame" in Theatrhythm consists of Dark Notes, randomly generated scores you can play solo or with friends. But the multiplayer here is almost nominal; it's what a child psychologist might call Parallel Play. There aren't many ways to influence your companions: you can make them lose, get or grant a duplicate of a higher quality drop, or bolster them with some skills. But you're both playing exactly the same game, mostly separately. And it's a missed opportunity.
I feel like there has a mid-point between a grand adventure and Theatrhythm's bus-friendly minigames; something on the order of a novella. I can't stop hearing melee classes banging on great foes along with the bass drum; black mages flitting in and out with the lead, white mages sailing on pristine strings. I hear Knights trampling through with the bass. Reconfigure the rolepaying "party" conceptually as a band and you start to arrive at some fascinating junctures the game only begins to imply. . Think about that for a little while, and you'll know why I haven't been able to sleep.