I'm a big fan of Shadow the Hedgehog!
I haven't played this game, but one thing I might want to highlight is the importance of focusing on plot for a Shadow the Hedgehog game (I'm speaking in general), because I feel it really makes the difference. What really brought me into past games with Shadow was the music, and the writing and characterization (despite still not being completely perfect in those games), as well as Shadow's one-liners. As a Sonic fan, I'm kind of just telling what makes Shadow as a game character special to me, though. Best of luck on the project.