To let the player select an optimal challenge level. Completing the game in a high difficulty levels in Quake or Doom was already the reward :) But looks like it is a high demanded feature. It's almost impossible to add some type of rewards right now - too many changes are needed, but I'll add rewards in my next games.
 "Berzerk Ball 2"){kind=icon}
 "Royal Warfare"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}
 "Frustration: Mouse Killah"){kind=icon}
To let the player select an optimal challenge level. Completing the game in a high difficulty levels in Quake or Doom was already the reward :) But looks like it is a high demanded feature. It's almost impossible to add some type of rewards right now - too many changes are needed, but I'll add rewards in my next games.