Normally I'm not super into add-on characters for playing SRB2. They might be gimmicky, OP, or just a novelty that wears off after a while. Normally, I'm not even interested enough to give a review. But this add-on is different.
The careful thought and balancing that went into this is incredible. The control is sublime and is just a joy to exist as. He's powerful and he does break some level design, but not any more than a vanilla character like Tails would. The difference is in the way Adventure Sonic breaks levels, where a character like Tails just slowly flies around, Adventure Sonic still has to maneuver dynamically, still making traversal exciting and fun.
This was clearly made with love and respect for the Adventure era of Sonic and what the gameplay style brought to the table while being considerate of how that fits into SRB2 level design conventions.
It's so well made it has become my defacto way to enjoy SRB2, and as someone who rarely wholly enjoys add-on characters, that's an impressive feat. Absolutely fantastic character add-on.