3D FPS

Proposed Modifications:

Add multiple additional levels and tie them in to create a logical progression in your game. (NOTE: Each level should be unique in some way, such as different type of challenges for the player.)

Add custom music to your game. (NOTE: Custom meaning you created the music with a tool such as Garage Band or Fruity Loops. If you just swap out the music for another track you find, this is not considered a significant change ... though you can do it without it counting as a significant modification.)

Modify the out-of-game menus in some significant and meaningful way.