It seems nobody has answered HonestGamer's question yet... I just completed the game for the first time on Normal difficulty right out of the box, 4 hours after installing it, no cheats or guides. I agree, the length is very disappointing.
Thank you! You are the first guys after days who has properly replied to my post!
I had to personally play this game to find it out. It was too bugy with random freezes and texture renderring issues. I uninstalled the game without having reached the end of the game - So much for the excellant series.