it's the worst genesis sonic, which is to say it's still pretty okay.
a handful of good levels (hydrocity one of the greatest) but mostly boring or plain old dogshit ones. my hottest take here is that the "& knuckles" half is more consistent in quality but the difference between the two isn't that big. levels like marble garden and ice cap stand out as some of my least favorite in the series, while oddly i was never bothered by sandopolis.
the presentation is very good, the art direction isn't as cozy/simple as sonic 1 or experimental as CD but it transcends sonic 2's goofy cartoon vibe almost effortlessly, if that's not your thing (it's not really mine!). i think SA1 is the closest the series got to recapturing this atmosphere and i don't think anyone would really argue that. and holy hell that soundtrack is probably an easy top 5 in the series

This was certainly a journey. It had many ups and downs...first, i want to start with the pros:

Soundtrack: I absolutely loved the soundtrack, they really added onto the experience and fit the theme of the stages really well, it is definitely the strongest soundtrack out of the classic sonic games.

Characters: The idea of having different storylines between sonic/tails and knuckles is really enjoyable and adds extra levels of replayability

Special Stages: I think the special stage minigame is exciting and captures a trial-and-error system well. Minus the fact I struggled against 1 stage for the super emeralds in particular it felt rewarding to get the emeralds. However, the way to get special stages becomes a con for me.

Shields: I love this system! The idea of having different elemental shields was so enriching for the experience. not only does it add an extra hit, but it also adds extra bits of situational advantages to the gameplay, such as the bubble shield adding water breathing and a BOUNCY effect to a lightning shield magnetizing rings to sonic and granting a double jump and resistance to electric attacks and lastly the fire shield granting invulnerability to fire-based attacks and granting a dash. The shields feel at home in this title, especially because of how HUGE the stages are in comparison to previous entries.

Boss battles: DEFINITELY the best bosses out of the previous entries, adding a variety of different gimmicks the bosses utilize the theme of the stages to grant a positive challenging experience. There is also mini-bosses in act 1 that are just as enjoyable.

CONS

Getting special stages: I didn't really like the idea of having to search all over an already huge act within 10 minutes to find giant rings to access these special stages. Sonic 2 had a system that rewarded players for collecting 50 rings and avoiding obstacles with precision once they reached a checkpoint to grant them the opportunity to get a chaos emerald that felt more natural and within the flow of a speedy game, this game. However, it forces you at multiple times to take it slow to check a wall that may break and reveal a big ring just so you may get a chaos emerald which just rubbed me the wrong way

Obstacle placement: I think some of the obstacles in this game were out to get me just outrageously, however not as bad as sonic 1 level design and sonic 2's Metropolis zone.

this is a really weird game for me
like on one hand its got a lot of really awesome bits and music and set pieces
like hydrocity for example is probably my favourite classic sonic level ever
but like also
its really annoying in specific parts (carnival night, marble garden) and that kind of holds it back a lot
its the best of the original trilogy, and while mania is probably better, i still kind of prefer this game over it anyways because
feelings are weird