Title says it all. Name a game that you forgot about for years but spent ages playing back in the day and let's discuss see who else played what! For me there's a couple:

Drakan The Ancient Gates - A Dragon and a Woman kill stuff action RPG style
https://www.youtube.com/watch?v=JKqI...jJYXnF3unR3e5q

Yaeger - Flight Combat sim on original Xbox
https://www.youtube.com/watch?v=k9RQlYlqi1o

Phantom Crash - one of the most fun games I played on original xbox outside of Halo 1 and 2
https://www.youtube.com/watch?v=JwNApZMTKj8