Whats the difference between this and Day of Defeat?
Day of Defeat is WW2 CS:S (Read: Total stuff).
Red Orchestra is a simulator on the Unreal engine. Where you get shot effects your performance, you must use Ironsights. When you rotate, your gun moves to new locations, thus making firing from the hip much more tactful rather than resourceful, and there's gore, tanks and Artillery strikes. Also, it follows the Russian armies rather than the UK or US.