Developer: Sonic Team
Released: 1998, Dreamcast
Sonic Adventure is Sonic's big step into 3D platforming, but depending on the person you ask, it may either hold up or be a step in the wrong direction. Nevertheless, it is a staple among the Dreamcast library even to this day.
A lot of content was removed during its development, including a giant mechanical dragon. Due to the game being rushed out for the holidays for its Japanese release, there's even more unused content found only in the Japanese release, as it hadn't been cleaned to make way for new content.
There are also many prototypes, the earliest of which contains a good amount of content either changed or deleted for the final version.