This game could benefit greatly from a cooperative campaign. Otherwise, the only replay value comes from doing the whole campaign all over again except at a higher difficulty. The "Authentic" difficulty is only unlocked after players beat the game, which removes all HUD elements from the screen (including crosshairs) in addition to significantly boosting the enemy's skill. There are also a few extras, like finding all the Killroys (some graffiti painted on the walls of every level) and completing them. This feature is probably linked to the Xbox 360's Achievement system, but PC players won't get anything except the self-satisfaction of finding them.
If you're looking for a good story and a compelling single player experience, and don't mind a few shortcomings or playing through the World War II setting yet again, Brothers in Arms: Hell's Highway is definitely worth the while.