Most military-themed games are either roller-coaster shooters (the Call of Duty franchise) or shooters with tactical elements (Rainbow Six); the original Operation Flashpoint fitted neither of those distinctions, as it was more of an "infantry in war" simulator. That is, instead of filling your screen with spectacle and flourish while leading you down a very deliberately-designed experience, Operation Flashpoint just placed you in the world with yourself, some gear, a mission objective, a detailed array of systems (movement, weapons, A.I., etc.) to consider, and the freedom to figure out how to fulfill your missions with your toolset. It was simultaneously hardcore, tense, unforgiving, and exhilarating at times.
So while the original developers have moved on to the ArmA franchise, Codemasters is trying to recapture some of OF's intense infantry-simulation magic with Operation Flashpoint 2: Dragon Rising.