If you look through the extras DVD in the collector's edition, you find out that they used motion capture for all the character movements, which is why they look more natural than a lot of other games.

Also, a hall mark of the crystal tools engine is that it can load the entire area at once by simply loading a set of resources which are replicated across the map. Downside is you get a copy-pasta landscape, but upside is that it is smoother and simpler to render, resulting in a prettier image.