I do wanna ask how you see Shadow- Is he a friend, do you trust him?
Hmph. Shadow.
I haven't had a lot of one-on-one conversations with Shadow, but I can definitely tell you what I think of him: he's egotistical, he's overly aloof, and needs to make up his mind on whether he's going to actually use his powers as the "Ultimate Lifeform" (yeah right) for something useful or just sit around whimpering about fifty years ago until he realizes he can do literally anything else.
All this to say, me and him aren't "buddy buddy" or whatever.
He's tried to destroy the world, and nearly succeeded, twice. Once upon a time ago he used to be good friends with someone like Rouge but now he acts like he doesn't need them. Why, you ask? Because he's over fifty years old, and elderly people tend to get bitter.
Am I going to deny that his involvement in many near-world-ending scenarios has turned the tides in our favor? Of course not. He helped stop the Biolizard, Black Doom, Neo Metal Sonic. When he finally decided to stop being lazy he actually helped with Infinite, who I hear pretty much became evil because of him anyway.
Okay, I'm rambling, so final answer: he's a useful companion, but outside of that, he's become nothing but another self-absorbed "ally" that thinks the sun shines out of his half-alien butt.