Being the first game, Sonic 1's style of level design would be reflected upon its many sequels to come, so it's just as well that it contains some truly original structural features such as loop-de-loops and extreme slopes and curves, the likes of which had never been seen before in a platform game, and set this one apart from the rest. Basic rules and methods of organising things that have been established here didn't change much throughout the nineties, and even after that, they're never too far away from modern games of the series, even when some of them like to shuffle things around a bit and try new ideas.

The zone/act system of game structuring is established here, whereby the six different, consecutive levels are called zones, differentiated from each other by their background locations and foreground visual features, pathway structures, specific interactive objects and of course, the music that accompanies them. These zones are further sub-divided into acts, which usually all share the same examples of those elements within the zone, but take place on a new layout map, and it's impossible to return to an area of a previous act after having completed it, during a single play through the game. There are three acts per zone here, although it's since become more customary for a zone to feature only two acts in most other games. These ones however are generally a bit shorter, and take place on smaller maps to accommodate for this. At the end of the third act for each zone, a boss battle takes place inside an enclosed space where you will take on Dr Eggman, who floats about in his Egg-mobile and dishes out a certain pattern of attacks that you need to avoid, and hit him with your spin attack jump eight times in order to fully complete the zone. This is the traditional structuring of a Sonic game that has been followed to varying degrees of loyalty by most other games of the series since. It contains very little in the way of story scenes, as most of the game's plot takes place in the form of a prologue that's not really contained anywhere within it. There are a couple of occasions however, such as the ending, where Sonic will be controlled automatically as a short, simple scene of events plays out that involves no dialogue whatsoever. Other than that, it's all action, and all you.

There's a great deal of variety across the six zones, many of which have since become pretty common level types. The nighttime cityscape with crazy looping and spiralling roads suspended in the air, the threatening factory environment, the pinball inspired zone that sends Sonic bouncing between bumpers, the cramped water-filled caverns and of course the hilly, tropical seaside paradise - all of these recurring environments throughout the series have their origins right here. What's also perhaps more evident here than in most other titles is the degree of variety in pace, regarding structural designs. Zones such as Green Hill and Star Light are custom built for speed, and can flow very naturally and really show off what's special about this game, yet Marble and Labyrinth Zones operate in a much slower, more puzzle-based manner such that they could be featured in any other platformer. Many would argue that these levels make the whole game feel slower than most of its successors, but I think it's this kind of variety that's crucial in Sonic level design, and it should never just be all about speed. As is far more common in 2D Sonic games than in 3D, many of the levels give you plenty of multiple routes, shortcuts, detours and hidden areas, so you'll always be able to find bits you've never seen before when replaying over and over again. As a child, I felt that of the four Mega Drive Sonic platformers, Sonic 1 was probably the overall hardest, thanks to the kind of nightmarish challenges you'll encounter in Labyrinth and Scrap Brain Zones. I would probably still agree with that now.

Also definitely worth noting are the visual aspects of the environments you'll encounter, and I feel that there is a certain abstract style to parts of Sonic 1 that set it apart from the others that don't quite match it. Such classic design touches as the chequered ground, folded-card style palm tree leaves and spiky flowers, random words illuminated in neon lights, and the obscure floating bird/fish patterns in the Special Stages have been replicated in certain ways, but there's just something about the way in which they've been used here that gives Sonic 1 a unique aesthetic quality all of its very own.

After taking a detour through the water-filled caverns beneath Eggman's base, Sonic pops back up to the factory to be confronted with the bad doc himself for the final showdown of the game! The appearance is the same as Act 2 of Scrap Brain Zone and you begin in an open room with a high ceiling. Walk to the right and past a low ceiling where you'll arrive in the final boss arena. That's right, there are no rings for this one, so if you get hit, you get dead. Fortunately the boss isn't actually as hard is it looks. You'll find yourself in a room with four large mechanical crushers, aligned on opposite sides; two embedded in the ceiling, two in the floor, and leaving a little open space on either edge of the arena. The crushers rest safely in their holes until any two of them are randomly selected to move into the arena, attempting to crush you into the floor or ceiling. They'll start moving slowly at first, so that you have just enough time to decipher which two are moving, and then step out of their way accordingly. You'll notice that Eggman has perhaps unwisely chosen to stand inside one of them, so if you're able to do so, quickly hit him by jumping and making contact with the side of the crusher that he is in. They don't hang around for too long.

On the final blow, both moving crushers will start exploding as they retreat, and the screen pans to the right where Eggman suddenly reappears, dropping from a tube and then running for his life to board his egg-mobile (which, as a one-off, is resting on the ground, on little legs for some reason). Follow him to continue the scene, and as he flies off, you can decide whether Robotnik retreats safely, or goes down in a flaming ball by getting one last, cheap shot in on him, just before you reach the edge of the path. Cut back to the Green Hill Zone where peace has finally been restored, as all of Sonic's little friends leap around happily while he does a victory lap over the hills. Sonic will eventually stop in an area, and if you collected all the six Chaos Emeralds during the game, via the Special Stages, they'll magically appear above him, and then disappear back into the wacky dimension from whence they came, also leaving the Green Hill Zone with extra flowers and taller trees. If you didn't collect them, Sonic will just stand there tapping his foot at you for a moment. Either way though, he'll then leap out at you in a victory pose, accompanied by the game's title, and followed by the credits. Credits don't feature too many names, so they also contain footage of the levels being played, some revealing more hidden bits and techniques you may have missed along the way (although not if you used this superb guide). After the credits we're shown a sprite of Eggman either juggling the remaining Chaos Emeralds or, if you stole them all from his evil grasp, throwing a comical tantrum on top of the word "End".