It's been clear at least since the Dreamcast era, if not further back, that Sonic the Hedgehog's console games were going to be in 3D. If you wanted old-school 2D Sonic, you went to the handhelds. Well, now the next Sonic game on handhelds is 3D, too.
Is this a bad thing? Maybe not!
To judge for yourself, take a look at the video above, which was shot by the good people from NTower at the Gamescom show in Cologne last week. It shows this fall's Nintendo-exclusive Sonic: Lost World running on a 3DS. Imagine that with the 3DS' glasses-free 3D effect turned on.
I dare say that a 3D Sonic on a handheld looks pretty good! Sorry, purists. Hey, at least the game has a mix of 2D and 3D gameplay. So it's not a complete departure from the old retro design.