Laconic / The Elder Scrolls IV: Oblivion

Go wherever you want and do whatever you want in a very big world being invaded by otherworldly evil forces.
Hero gradually descends into madness after watching their best friend die in front of them.
Stop right HERE criminal scum!

http://tvtropes.org/pmwiki/pmwiki.php/Laconic/TheElderScrollsIVOblivion