I'd like to see a sequel from this game but a GOOD one, I remember when I was on the Gamecube era I bought this game just to see how it was and that time I thought it was pretty fun but by just looking at it now it's just bad, now here are a few ideas that would be on the sequel if there was one:
Now more paths: Depending on how you do or what you do in the game, like choosing being good, bad or neutral, I know it could take you to different levels and multiple ending but no, it was complicated that time doing a good mission but then failing many times and just doing the other one you just can.
No more sidekicks: Shadow is good by himself and he rather be by himself, does he really need people to go with him? Like other characters from the Sonic series and villains, I mean they are just worthless, they don't even help you and sometimes they just jump and fall somewhere where they die until they respawn or get replaced by another character.
No more bad dialogue: The dialogue could be really cheesy, very repetetive and badly interrupted by another character in the first game, just make it better without those things!
No more multiplayer: <---Like what it says, unless it's good this time.
Language: In the first game there were a few swear words like shadow kept saying heck, damn and for some reason a part where Sonic says **** I think, come on it's a kids game (kind of) if it will follow up like that make it a T rated game, unless some censor could give it an E10+ rating again.
Weapons: In the first game the gun shadow carries wasn't really as good as everyone expected, you can just jump to enemies too, at least give some new better guns and a better use of them or just no more guns.
Storyline: Where was Shadow being lately? You guys can still make a new story about him other than just a follow up of how he had amnesia, new bad guys and her Maria.
BE GOOD: Just be good.
Shadow the Hedgehog is my favorite character from the series and I can just stare at how bad his first game as the main character was, it was as bad as how bad Luigi's first game was, Mario is Missing, but then he returned in Luigi's Mansion which turned out to be very good as a return. Just make another game starting Shadow, it doesn't have to be a sequel of his first game but just any new game starting him as the protagonist..