If you look at the history of video game characters, you'll see that they evolve over time in both style, and appearance. That goes double for Sonic the Hedgehog. For as you look at his original art, and how he is now, there is a world of difference. And not just that, the original Sonic was more of a 2D speedster, while the modern Sonic mainly traverses 3D worlds. Well, for the first time ever, you get to pick which Sonic you want to be in the ultimate celebration of Sonic the Hedgehog! This is Sonic Generations.
This is a tale of time itself, as someone is creating time holes, ones that lead to the past. And when the modern Sonic and his friends enter these time holes, they find themselves looking at some very familiar faces, including a younger Sonic the Hedgehog! But, when their friends get captured, it's up to these two Sonics to free them, save the day, and right what is wrong in the timestream.
Sonic Generations is a celebration of the character from start to finish, including the worlds and areas you visit, how you play them, and the fact that you can choose past or present Sonic to play as. As you advance, you'll get to unlock more and more areas to play in, and by extension to have fun in. You'll get to see past worlds remade in 3D, and relive classic levels in a new way. Add that to legendary villains returning to face the Sonics, and you've got one grade-A adventure just waiting to be played.