DO NOT change any quality settings through in-game configuration. i.e Shadows Quality, Effects Quality, etc.

Tweak your resolution scaling:
Open GameUserSettings.ini and set sg.ResolutionQuality to your preferred resolution scaling.

Tweak your Luminosity setting:
Open Engine.ini and set DisplayGamma to your preferred settings.

The game is too dark?
Open Engine.ini and change r.Tonemapper.Quality=3 to r.Tonemapper.Quality=0. It will give you minor performance boost.

Enjoy!