@DarkInferno :
Totally agree with you ! Rewards , upgrades are a way to keep motivated the player to play to the end of the game.
Ubisoft understood it with assassin creed, the next episode will include upgrades and rewards to find when completing special indoor dungeon levels.
COD4 , also have rewards (perks) , and personnalisation throught the perks : you create your own skills.
And that's what makes games like Bioshock or Follout 3 so successfull !

Even makers of Gears fo War series recognise that future of FPS will go through personnalisation, customisation and rewards like power ups, skills etc ...