The game has three distinctive difficulty modes which can only be accessed by creating a profile. The modes are Sergeant, Sergeant Major, and Authentic mode. Each mode has it's own set of differences to make gameplay more challenging, differences as follows:
Sergeant: Easy, minimal enemies and few scripted AI events. Full HUD is visible. Sit reps are very common (i.e first chapter has one a street away after the first one, after assisting Bradley)
Sergeant Major: Fairly challenging on some missions, additional enemies will spawn in certain locations, making venturing into unknown areas very risky. Sit reps are less common, but still present making chapters manageable.
Authentic: This difficulty removes the HUD entirely, leaving only the "D-pad" interface on the bottom left. All enemy markers are gone. Even more enemies have been added to the games chapters, with additional scripted enemy events. This mode also removes sit reps entirely, if you loose two soldiers at one time (usually happens in one go it seems), you restart the mission from the start.