Well, i actually have the game already and played it and i thought the same, but surprisingly its kinda slow/laggy, i've tried setting to high, same speed, set some to medium, same speed, then even set grass and sky to low, just a little bit faster, WTF!
Might want to try fiddling with the shadows setting, they tend to be a resource hog in many games.
Otherwise, make sure your drivers are up-to-date, you´ve got nothing running in the background, etc. The usual stuff. --- when anything that's anything becomes nothing that's everything and nothing is the only thing you ever seem to have