I'm at work and will be going to the casino straight from here tonight, so I can't check this until tomorrow.
I just read that there is a glitch while fighting Raam that is you shout into your headset, it will trigger the cutscene and beat the game.
Someone please load up the last portion of the game if you've already beat it and let me know if it worked. If possible, try on all three difficulty settings.
I personally think it's a crock of ****, but you never know.