This is one of, if not THE, best character mod I have ever played. Inazuma and Aether both control very well, their Super and Sol forms are great to run around with, and I managed to beat the regular campaign as them. I do however, have some issues with the secret content.
*SPOILERS AHEAD*
Mindscape Zone is a pretty decent challenge... is what I would say if you didn't only get three lives to start with on top of all the bottomless pits, and trying to master the Homing Attack and Bolt Stream abilities.
Facciolo is stupid to fight since you hardly have any rings, and if you manage to smuggle in a Super form to fight the guy, his attacks pierce through Super forms similarly to Big Arms from the original Sonic 3. Why?!
I just straight up gave up trying to unlock Ultimate Inazuma without beating Mindscape Zone because of Facciolo alone. I mean, does he have to be this difficult? I'd rather play the final bosses of Sonic Superstars. That's saying a lot because the community disliked those bosses due to their difficulty.
Overall, incredible characters, bullshit secret content. I would give it 5/5, but Mindscape Zone and Facciolo drop it down to 3/5. I'm sorry.