This is definitely the first game in the series. While the version included in Sonic Origins Plus has many enhancements, like the spin dash, drop dash, 16:9 support, it still isn’t as good as Sonic 2 or 3K. The name of the game is speed, but many of the zones aren’t built around it. Hell, as soon as you’re out of Green Hill you’re in Marble Garden, my least favourite and slowest level. It’s still a good game and still holds up, but the others are so much better.