>>535313293
They wanted to make something to release along with Sonic 3. They decided remastering Sonic Generations while adding on a Shadow portion would be the best course of action. Shadow Generations has Shadow fight enemies from his past, a lot like with Sonic Generations. Shadow Generations is more story-heavy and tonally darker. It features a lot of physical and mental distress for Shadow, since he sees Maria and Gerald again, but it still remains pretty kid-friendly. Black Doom returns, and Shadow is given new transformations/powers called "Doom Powers", which feature unique gameplay.
It doesn't add a ton of "new" content if you've played the 00's games, but neither did Sonic Generations. It's a decent play.