Plans for a sequel fell through after a Lawsuit was filed to Sega by Ex-Sonic comic writer Ken Penders due to the Marauders resemblance to his Dark Legion characters from the comics. Additionally Bioware was bought by EA and they had no Interest in the project. So this game is left on a cliffhanger and rendered non-canon. It's also because of this Lawsuit that Shade and the Marauders are never brought up in the series ever again, Despite Shade still being with Sonic when the game ends.
This is the first (and only) RPG in the series.