Personally, my favorite is Disgaea, followed by La Pucelle and then by Phantom Brave. (I haven't gotten Phantom Kingdom yet.) I tend to favor story, which is why I liked Disgaea (whose story is kind of fluffy, but still pretty good) and La Pucelle (which has a nice beefy, though perhaps more typical RPG, story) over Phantom Kingdom (whose story underwhelmed me). Still, they're all good games, and very meaty gameplay-wise.
As for why IS was never licensed, that's kind of a tough question because there are SO MANY reasons:
1) Objectionable themes. This is probably the major reason why. Off the top of my head, you have: teens attacking their principal with weapons; a possible lesbian relationship involving one of the main characters (Yukki/Anna); a possible gay relationship involving THE main character (Tatsuya/Jun); drug use by one of the main characters; the return of Adolf Hitler and his Nazis; terrorist bombings; et cetera. Not to mention that the ending is kind of a downer.
2) Problems with localization. I believe that a lot of the time the American localization team will have some cooperation and involvement of the original developers. When they were first looking at releasing it, however, this was impossible, because the development team was already hard at work on Eternal Punishment.
3) Outdated graphics. If they'd released Innocent Sin, by the time they localized and released Eternal Punishment its graphics (with no noticeable improvement over IS) would have been considered outdated in the marketplace. (Well, even more than they already were. Though, to be fair, it's still a damn sight prettier than Dragon Warrior VII.)
eikitty has a good article on the problems with a domestic release kind of buried in the Oracle of Maiya FAQ - here's a direct link to it (http://yoridori.org/oracle/tsumiusa.txt).
no subject
As for why IS was never licensed, that's kind of a tough question because there are SO MANY reasons:
1) Objectionable themes. This is probably the major reason why. Off the top of my head, you have: teens attacking their principal with weapons; a possible lesbian relationship involving one of the main characters (Yukki/Anna); a possible gay relationship involving THE main character (Tatsuya/Jun); drug use by one of the main characters; the return of Adolf Hitler and his Nazis; terrorist bombings; et cetera. Not to mention that the ending is kind of a downer.
2) Problems with localization. I believe that a lot of the time the American localization team will have some cooperation and involvement of the original developers. When they were first looking at releasing it, however, this was impossible, because the development team was already hard at work on Eternal Punishment.
3) Outdated graphics. If they'd released Innocent Sin, by the time they localized and released Eternal Punishment its graphics (with no noticeable improvement over IS) would have been considered outdated in the marketplace. (Well, even more than they already were. Though, to be fair, it's still a damn sight prettier than Dragon Warrior VII.)