When is a sequel not a sequel? When it's Sonic The Hedgehog Part Two, that's when.

The second and last part of Glu's serialisation of the classic console hit from early 1990s, Sonic The Hedgehog Part Two is a pixel-perfect rendition of the game that made Sega a household name. As such, it introduces new levels but nothing else that you won't have seen in Part One.

In case you missed the first half, here's a précis of what's happened so far: Sonic, a spiky blue hedgehog, has taken umbrage at the evil Dr. Robotnik's plan to enslave the land's various animal inhabitants by encapsulating them in suits of armour and setting them loose to pillage and plunder.

Sonic, being a socially-responsible sort, embarks on a quest to free his furry friends and put an end to Robotnik. Playing as Sonic, along the way you'll collect rings, too, with one hundred bagging you a ticket to the psychedelic bonus stage where you can net extra lives and the mysterious chaos emeralds.

It all adds up to a sideways-scrolling platform game that's smoother and more fluid than anything you'll have played on your mobile phone to date.

Sonic The Hedgehog Part Two harks back to an age when a platform game's complexity came from the levels and obstacles you had to overcome and not the control system.

An exercise in simplicity, you can run left or right by pressing in the appropriate direction on your handset's directional pad. To jump you press up and duck by pressing down. Destroying the armoured inhabitants of each level is achieved by jumping on them, or by racing along and pressing down to curl into a spinning ball of spikes, running them over.

That's it. It's wonderfully simple, like all classic platform games are. But what set Sonic The Hedgehog apart from the crowd was the speed and the way it was represented on screen. Put plainly, it's fast, and that speed plays a key in many of the levels, which incorporate loop-the-loops, ramps and other stunt-inspired furniture.

So, the question is: if you've got Part One, what can you expect from Part Two? The short answer is: more of the same. That said, the three different zones that are visited in Part Two are very different animals, starting with the challenging Labyrinth Zone, the majority of which takes place underwater. For this reason it's worth shelling out for if you enjoyed the opening instalment.

These three zones are the last three in the original game and they represent the stiffer end of the difficulty level, too. If you've not played Sonic The Hedgehog on mobile yet, we strongly recommend you begin with Part One for the sole reason that it starts gently and gives you a chance to get used to the game's challenges.

Whichever camp you fall into, this game is an essential title if you enjoy platform games. Don't worry that it's essentially a fifteen-year-old game. Sonic The Hedgehog is as fresh today as it was when it launched and is a marvel on mobile phone.