Playthrough was done using the Sonic 3 A.I.R. PC port of the game.

Sonic 3 & Knuckles (formally informally named after the fact that it is quite literally the two cartridges, Sonic the Hedgehog 3 and Sonic & Knuckles stacked on top of one another in the Genesis fusing to make one continuous game) is actually, surprisingly enough, a great Sonic game, and a really good and ambitious 2D platformer at that too, filled with some of the best Zones, music, mechanics and flare the series has seen thus far and really just feels like a perfected vision of what the classic Sonic series has entailed, sometimes lost, shoved away or gotten halfway through. (lookin' at Sonic 2)
This is most likely the result that, again, it's two games combined into one, neither of them would be really complete if it wasn't for the other and if you were to take Sonic 3 or Sonic & Knuckles separately you'd notice how incomplete they are alone, but together in one long run makes for a hell of a good time, I especially like how throughout all of it in both halves the Zones remain really consistent and have fun themes and gimmicks to them, also how much they balance actually going fast whilst traversing through obstacles and platforming, having just enough of both where every stage isn't simply just a mindless breeze or is needlessly complicated, all, of course accompanied with some of the greatest bangers that make use of that soundchip to no end, that first Sonic 3 half of this game is just pure magic, and this is is coming from somebody who doesn't really prefer Sonic over other platformers of the era.

Other than that, the rest of the zones specifically in the Knuckles half are a bit of a mixed bag AND Sandopolis Zone, but nothing really bad, this part of the game is really reserved for the expansion of Death Egg Zone and a bunch of the things leading to the ending, which is cool to see the series taking its crumbs of story somewhere at all considering this is the time they introduced Knuckles making the main trio which then would become the face of the series practically. As somebody who comes from kinda playing some of the later entries in the series, it's nice to see that they had a foothold in a game as polished and clean as this one... Only makes me wonder what went so wrong after, hmm...