Shadow the Hedgehog is a game in the Sonic series, that is famous for many things, such as it trying to be more edgy, the "hero" and "dark" missions, and much more.
The story starts up after Sonic Adventure 2, where Shadow has amnesia here. He met a new character named "Black Doom", who wants Shadow to collect the chaos emeralds to give to him.
The gameplay is similar to the other Sonic games, but with some exceptions. One of which, introduces guns to the sonic series, and there are many guns, one of them, being an Egg sucker, (as a reference to Billy Hatcher and the Giant Egg). Other new elements include vichielces (which do return in Sonic the Hedgehog (2006)) and the "Hero", "Neutral" and "Dark"system.