Who can remember when this was all just fields? Shiny, stripy, bright green fields, lying under fluffy white clouds and skies bluer than the liquid in an Always ad. All right, it wasn't all just fields; there were neon-lit casinos, crumbling ancient temples and cities in the clouds, too.
Yes, there were also giant industrial complexes so huge their purpose was probably something to do with chemical warfare and Iran. But these were fun to explore, so long as you could keep from drowning in the rivers of toxic waste.
And who inhabited these wondrous worlds? Not zombies, Nazis, mutants or drug dealers. Just a blue hedgehog, some small furry animals trapped inside robots and a fat man in a space helicopter. Good times.
But then it all went wrong. The Sonic series failed to make a successful transition into the brave new 3D world. Seeing our hero struggling round environments he wasn't designed to inhabit was painful, like watching your Grandma try to find a nice comfy pair of slippers in Urban Outfitters.
SEGA tried to paper over the cracks by introducing new characters, as if a slutty rabbit and a stupid crocodile would be enough to distract us from the truth. Then there were the experiments with role-playing and racing. Most recently, there was some ridiculous nonsense about werehogs and an attempt to shoehorn Sonic into the world of Arthurian legend. Inexplicable.
Even SEGA recognises things have gone wrong. The company is currently busy removing the worst of the Sonic games (all the ones produced this century, then) from shop shelves in an attempt to pretend they never happened, like Stalin airbrushing Trotsky out of photographs.
So it's a bit much, on booting up Sonic the Hedgehog 4: Episode I, to be greeted with old blueface grinning away on the menu screen, wagging his index finger as if admonishing us for some naughty misdemeanour. We're not the ones who have been rubbish for the last 15 years, mate.
But a few minutes later you'll be ready to forgive Sonic anything. Yes, even the hoverboarding incidents. That's because you'll be speeding, spinning and soaring around glorious 2D environments, across green fields and between fluffy clouds, pausing only to collect power-ups and bop robot fish on the head.
Sonic 4 isn't just a return to form; it's an apology for having been away so long. The differences between this and the old Sonic games are so few and far between that playing it involves existing in a constant state of deja vu. Which, if you were a fan back in the day, is a good thing.
Even the plot's familiar. Once again Sonic and Dr Eggman are fighting over the Chaos Emeralds, the most hotly contested artefacts since the Elgin Marbles. You start out in the Splash Hill Zone, which is basically the Green Hill Zone in HD.
Other zones are based on the classic casino, ruined temple and industrial zones. Before you accuse us of spoilering, they're all unlocked as soon as you complete the first, super-easy Splash Hill level, so you'd find out soon enough anyway.
Miserable old purists might complain about this. In ye olde Sonic games of yesteryear, death was final. Even if you'd made it to the last level you had to start again all the way from the beginning. This, the miserable old purists would say, taught children a valuable lesson, namely that life is nothing but a series of repetitive actions punctuated by crushing setbacks.
But times have changed, and you could no more convince 21st-century kids that starting from scratch is a good thing than you can make them understand that the Victorians didn't have mobile phones. Sonic 4 features new-fangled online leaderboards where you can compare your times and scores, so the option to select any level is essential. Plus, it means you don't have to keep hammering away at the same old section when you get stuck.