Balance. I spent a good deal of the extra time playing the game with different types and levels of characters to test the difficulty of the game. Because the game is non-linear, it's very possible that a low-level character can wander into areas that you might not have imagined they could have reached. Our clever testers frequently surprised me when they showed up in the deepest, most dangerous areas with relatively low-level characters, using such skills as sneak to get past obstacles.