Sonic Adventure 1 is better in every way than Sonic Adventure 2 (excluding music, it's even in that area imo), and it understands Sonic's design philosophy much more. Sonic Xtreme would've been a terrible game if it released, and it would've been a stain on the franchise at the very least. Sonic CD takes place after Sonic 3 & Knuckles. Sonic 3D Blast is a good game, it's just that people are playing it like as if it's a Sonic game and not a Flicky game. Knuckles' Chaotix's tether ring mechanic could've been an awesome mechanic in single player if they polished the controls. Sonic and Knuckles is a better standalone game than Sonic 3 Alone. Sonic 2's art style is just a jankier version of Sonic 1's art style imo Sonic 1 has the best looking pixel art out of the classic games.
Sonic CD is simultaneously overrated and overhated, sure it has its positives which definitely deserve praise but the execution left me wanting something more polished. Sonic 3 isn't just better than Sonic 2, it's a replacement in almost every way. Sonic 1 is better than Sonic 2 because the level design is more polished and fair even if the pacing is arguably less consistent.