So people are just excited to see a character they like in the movie?

Yes, but Shadow’s appearance in Sonic 3 is a bit more significant than that. For a few years, Shadow was one of the faces of the franchise, and came second only to Sonic in character popularity polls. His story was complex, his character intriguing, and he was an excellent foil to Sonic’s happy-go-lucky attitude. Following Sonic ‘06, Sega made a concerted effort to pull back on the ensemble cast in favor of going back to basics. Sonic was the only playable character for most games, the stories became more simple, and everyone was sanded down to a few distinct traits, with Shadow being solely defined by broodiness and hating the company of others, despite making some really excellent strides in accepting the companionship of the rest of Team Dark in ‘06

For nearly 20 years, Shadow has swayed in the background as a caricature of himself, and Sega has taken its time putting him back in the spotlight. He made brief appearances in Sonic Forces as a DLC character and had a bit part in the Sonic Boom subseries, so Sega has been gradually nudging him back into the public consciousness. But what we’re seeing in Sonic 3 seems to be leaning toward a version of him that we haven’t seen in years. Shadow the Hedgehog deserves more than being remembered as a misanthropic edgelord who said “damn” and used a gun one time. It seems like Sega, and hopefully the rest of the world, is finally coming around to that fact.