In Sonic Generations, someone or something is eating reality, and it's creating holes in time. It's so bad that Sonic finds himself in the "white space," a completely empty void of time that allows him to transport to different time periods. Technically, he's not alone. Sonic is joined by an older, pudgier and more '90s version of himself, the classic Genesis version of Sonic the Hedgehog. Together, the two have to travel to their old adventures and find a way to fix time.

The first of the gameplay modes, Classic Sonic, is a throwback to the older style of Sonic. As near as one can tell, he's designed to look and play as much as possible like the Genesis version of the hero. There's no homing attack, just jumping and the spin-dash first introduced in Sonic the Hedgehog 2. What stands out about the mode is that, unlike Sonic the Hedgehog 4, a lot of effort appears to have been put into replicating the older game style. Whereas Sonic 4 was more of a hybrid of the classic and the modern, Sonic Generation's Classic Sonic mode wholeheartedly embraces the classic feel. While it may be disappointing to people who enjoyed the Sonic 4 take on the 2-D gameplay, the only significant difference that I noticed is that you could press the X button on the Xbox 360 controller to instantly rev up your spin-dash, instead of having to use the duck-and-press-jump method from the older games. It's worth noting that it isn't identical to the older Sonic titles, though. There are some new gimmicks and abilities, such as one stage where classic Sonic utilizes a skateboard that somewhat alters his gameplay.

Modern Sonic, on the other hand, is the embodiment of everything from Sonic Adventure onward, although he most closely resembles the more polished and refined version of the character from Sonic Unleashed and Sonic Colors — minus the Werehogs, swords, psychic hedgehogs from the future and so on. While the focus of Classic Sonic is on "speed as a reward," the modern version of the character is more about high-intensity speed all the time. His levels are a mix of 2-D and 3-D, but even the 2-D sections have a much greater emphasis on speed than classic Sonic. While modern lacks some of the gimmicks and powers he had in recent games, he does maintain the expected modern Sonic powers. He can perform a homing attack on enemies, grind on rails, sidestep and earn Boost Gauge so he can blast through enemies and obstacles without pausing.

The levels are not just divided among classic Sonic and modern Sonic. Instead, each of the levels has a version for each of the two Sonics. Take, for example, the opening Green Hill Zone. For classic Sonic, this is a remixed version of the classic level from Sonic 1. It's not exactly the same level, but it's close enough to hit all the nostalgia buttons, right down to having the same music. For modern Sonic, the level is completely different. There are speed boosts, rails, sections where you have to use the homing attack and even a callback to the infamous Orca Chase sequence from Sonic Adventure 1. Even the music is different, with Green Hill Zone's classic tune being remixed into an intense techno version that more closely matches the modern Sonic gameplay.

The general idea is to include levels from both classic and modern Sonic games. While there are clear references to classic stages, they're not going to be the same. Even if you play as modern Sonic in a Modern Sonic stage or classic Sonic in a Classic stage, you're going to get a new experience with new enemies, new dangers and new tricks.  The stages are inspired by the older stages but are clearly not exactly the same levels. It's sort of a "greatest hits" version of the stage, with a lot of the cruft trimmed to leave only the most iconic parts of the level.

The recently announced City Escape stage is a great example of this. In Classic Sonic, the stage is completely new but has a fair share of references to the original level. For example, classic Sonic has to contend with the evil GUN truck that chases after Sonic in the original Sonic Adventure 2. Even if he's just a little fast, the truck will destroy the geometry of the stage and force Sonic to take different routes. The level also has a slower, jazzier version of "Escape from the City" by Crush 40 and no Eggman robots, so it's very clearly a Modern Sonic stage. There are grind rails, but classic Sonic rolls them down like a slope instead of grinding them. Even the general aesthetic is very different from the older Sonic style. Despite this, the gameplay feels more like a Genesis game than a modern game, even the 2-D Rush titles.

The Modern Sonic version, on the other hand, initially looks a lot closer to the Sonic Adventure 2 iteration of the level, but the similarities don't last very long. You begin the stage skateboarding down the street, just as you did in Sonic Adventure 2, but the skateboarding segment is longer and features different obstacles and mechanics. Once you leave the skateboard, the level contains many similar obstacles that have been remixed and revised. The biggest change comes during the GUN chase at the end. In Sonic Adventure 2, it was a straightforward chase, with the GUN truck tearing down the street as Sonic tries to stay ahead of it. In Sonic Generations, the truck gets an upgrade so it has chainsaws that burst from the back of the truck and try to saw Sonic to pieces. Even a jet engine is installed in the back so it can drive up a wall and chase Sonic even when he's defying gravity.

Sonic Generations looks to be the best of both worlds. The classic Sonic stages are fun in a way that calls back the nostalgic fun of the original Genesis titles. The modern stages look to be a solid refinement of the formula introduced in Sonic Unleashed and Sonic Colors. The gameplay isn't changed much, but in this case, that's a good thing. There's something here for everyone who likes Sonic the Hedgehog games.