This first sequel gave us our first secondary character, but we can put up with Tails. He's alright really, and doesn't do anything here that Sonic can't do (he can't even fly on command), which is probably why he works. There's an improved Special Stage with pseudo-3D shenanigans, a greater emphasis on speed, better graphics, another incredible soundtrack… it is an improvement in every respect.
Sonic 2 also gave us the spin-dash – perhaps the only extra move the original game would have benefited from. There's even split-screen two-player mode, which was the only criticism anyone seemed to have of the original, although it's squashed and riddled with slowdown. Not that we didn't play it to death, mind.
Above: Tails follows you around and is pretty useless, even getting in the way during boss battles. But you can 'switch him off' in the options
In essence, Sonic 2 is more of the same, just bigger, bolder, louder and faster - possibly how the first game should have been done. The three-act levels have been mostly shortened to two acts, allowing for a greater variety of zones to blaze through in the same amount of time. The enemies play less of a role – a theme that was set to continue with subsequent games, but still retain most of the imaginative design of the original.
When Sonic is hurtling around the screen, it could be criticised for 'playing itself', but you still feel like you're in control. You can screech to a halt or jump away from the plotted path if you want, you just won't want to stop the rush that's threatening to melt your TV screen.
If Sonic 2 had never been released and instead was coming up for release now, we would be incredibly excited. And assuming the two-player mode was fixed and it was all HD and everything, it would be everything we'd been longing for. It's the most user-friendly of all the Sonic games, beautifully presented and still a challenge if you want to complete it properly. If you haven't played it, then do so right now. It's a joy.