The juxtaposition is going to be be phenomenal.

Sonic Generations: Let's go do this adventure thing! Oh, hey, cool, our past selves! Nifty, a monster for us to fight! Enjoy your future, past me, (shoves Shadow 2005, Sonic 2006, and various other terrible games into the closet) it's gonna be great!

Shadow Generations: (Shadow trying to stop himself from breaking down sobbing over the death of Maria as mental images come unbidden to his mind about what their lives on earth might have been like, whilst traveling to the ARK in order to confront his creator, Black Doom, an enemy he thought long dead. Upon arriving in the White Space, he is finally afforded the opportunity to speak to both Maria and to his father Professor Gerald again, from a time before Maria died and Professor Gerald went mad with grief.)