Having now finished every Persona game with the exception of Eternal Punishment, I can say that they are all amazing experiences (except for SMT: Persona, which is okay), especially Innocent Sin.
The characters are some of the best in the series. My rank for the best characters across the Persona games now goes: P2 > P3 > P4 > P1. Maya, especially, is one of the greatest characters in the series and it's unfortunate she didn't even rank in the top characters in the Persona series from the Japanese fans. All of the major Persona 1 references in P2 were also nice to see, especially for someone who played the game before playing its sequel.
The presentation in general is well done. One of the main reasons I feel Persona 1 had the most unremarkable characters was because they all had static portraits and their models barely emoted. In P2, characters have tons of expressions portraits—even the unimportant ones—and they emote during scenes in a way that makes them come to life better than how they just stood around in P1. The music's awesome, as to be expected, but there's also so much of it in the remake so songs don't feel stale.
The only problems I have with IS are that the demon encounter rate and the contact system. The encounter rate is a bit too high and there aren't many options to reliably flee from battles, so walking a few steps between each battle in a dungeon can get quite tedious.
I like how they developed the contact system—the method to converse with demons and gain their cards to obtain new Personae—compared to P1 to be able to execute duo/trio contacts, which often gives entertaining results, albeit repetitive. What I don't like about it is that it's like another form of grinding, where you need to memorize what to say to certain demons to satisfy them and do it over and over again to get their cards. The card system is an interesting twist on the Velvet Room fusion system that is different from all of the other Persona games (where cards of the different Arcana are fused to obtain new Personae instead of demons/Personae themselves) and I think that the contact system is more interesting than the weird "Shuffle Time!" system that's in P3 and P4.
That said, the story is the best thing about the game for me and the ending is excellent. What I wonder is how well does Eternal Punishment compare for those who've played it? Does the story take place immediately after the ending of Innocent Sin? And making Maya Amano a silent protagonist sounds like the worst thing they could have done. I really hope they bring the PSP version over to North America at some point, because this experience feels rather incomplete without it.
This also makes makes me wish that P2 had at least a small presence in Persona 4 Arena.