In the US, the ESRB has rated OFP "M" for mature audiences (17+), describing it as containing blood and violence. In Europe, the ELSPA rated OFP at 15+. Does that mean that European teenagers are more mature than their American counterparts? Sorry I asked!
Besides violence (guns are shot, bombs go off, people die) and bloodshed (red puffs appear when someone is shot, blood stains and possible disfiguration are shown on dead bodies and puddles of blood were introduced in OFP: Resistance), there is a very trivial amount of mild profanity.