In-game GUI that allows to quickly configure engine graphics options that are not listed in common game settings, but can only be accessed from console or user.ltx file.
Default Tab key opens new menu. Another key can be assigned right there, in the opened menu.
Render values that are vital to set correct lights and shadows: tonemap, lumscale, bloom (also there are gloss factor and parallax height). Play with settings until you feel satisfied with picture. Check out Default button, see if those values are good enough to start from.