Shadow characters are kind of a fun addition but really they're just situationally slightly better/worse versions of the same characters most of the time. The game stands up enough on its own though; the characters are unique and fun and the music is good too. I wish the attacks had a little more oomph though.
This game takes what the previous version did and adds so much more. In addition to the arcade styled story modes, there's an entire traditional story mode that's genuinely super interesting. Sho Minazuki is another great character who retroactively makes Ikutsuki from P3 a better character, even though he's still pretty unremarkable at the end of the day. The cast of playable characters is about as deep as it could be for the source materials.