Sonic & Knuckles is hitting XBLA on September 9 and it will indeed include the cart stacking bonuses of the classic original title! Sega is throwing in the bonuses, but you do have to have the original games on XBLA first for it to work.
With Sonic the Hedgehog, you’ll unlock the “Blue Sphere” bonus Chaos level from Sonic the Hedgehog 3. If you own Sonic the Hedgehog 2, then you’ll be able to play as Knuckles in the game. Playing as Knuckles will let you reach areas that Sonic can’t reach and will include new power-ups too. And with Sonic the Hedgehog 3, you’ll be able to play the game as Knuckles and the design of the game is changed so the experience between Sonic 3 and Sonic & Knuckles feels seamless.
This is extremely awesome of Sega to do. This is how you do fan service and it kind of feels a little like the Genesis days.
