This is the combined version of Sonic 3 and Sonic & Knuckles. I mentioned in my reviews for both of those that they feel incomplete on their own. The reason is that they were planned to be one game, and it ended up having to be split due to time and cartridge storage constraints. This game does not have that problem; there's no weird cutoff point or awkwardness in the beginning. This ends up combining a lot of the best features of Sonic 3 and Sonic & Knuckles while also smoothing out some of the rougher edges. The bad points in S&K don't feel as bad here because you're more ready for them. This game does also change some features from S&K: in particular, the function of the special stages in the second half of the game. If you already have all the chaos emeralds before you get to Mushroom Hill Zone, then the special stages you do from there onwards upgrade them into the super emeralds, which allow you to become Hyper Sonic. This feels much more rewarding than just getting the chaos emeralds from these because the special stages in the second half are noticeably harder than the special stages in the first half. In S&K, this just felt a little jarring, but here, it works because an even better reward is locked behind them. Individually, Sonic 3 and S&K aren't as good as Sonic 2. The combined version, however, blows Sonic 2 out of the water. I strongly believe this is the pinnacle of 2d Sonic, and it's one of my favorite games I've ever played.

Like with Sonic the Hedgehog 3, this game definitely feels incomplete. Unlike with Sonic 3 though, you can tell right from the beginning. Mushroom Hill Zone does not feel like the beginning of a Sonic game. It's a really good zone, but it isn't a starter zone. It definitely feels more like a midpoint. Something else that bothers me about this game is the general level quality. Sonic 1 and 2 are both good, but they both have some complete BS in there somewhere. That BS was largely absent from Sonic 3, and the reason is because it's all in here instead. Sandopolis Zone Act 2 and Lava Reef Zone Act 2 are both incredibly annoying. Fortunately, I felt those to be the only bad levels. There's also something this game does very well that Sonic 1, 2, and 3 do not: the ending. I had a blast playing the Death Egg Zone and the Doomsday Zone. Overall, this is not as good as Sonic 2 or 3, but it's still a good game. However, I'd recommend playing Sonic 3 & Knuckles instead for the full experience.

The concept of a more momentum-based platformer is one that I like, and I think this game does a decent job as one. The levels that utilize this concept effectively do it really well, and it makes speeding through levels surprisingly fun. However, not all levels use this concept well. Marble Zone, Labyrinth Zone, and Scrap Brain Zone all seem a little too slow for what this game was going for. The final boss was also a bit underwhelming. It wasn't particularly hard, and it doesn't really make you feel like a badass when you beat it. Overall this is a decent game and a fine start to the series, but there's a lot that could've been improved.