3. No Russian - Call of Duty: Modern Warfare 2
No Russian had a great deal of controversy surrounding it when MW2 was released. You take control of a deep cover CIA agent who joins a group of Russian ultranationalist terrorists who go on a murderous rampage through an airport. The player is allied with the terrorists- however, you can play through the mission without killing any of the civilians. The civilians however run in terror and attempt to crawl away, leaving a trail of blood in the process. If you decide to be a true good guy and kill the terrorists, you'll fail the mission too. You are warned at the start of the campaign though of the mission's disturbing content and can opt to skip the mission entirely. If you chose to go ahead, you can still skip the mission at any point. At the end of the mission- the leader of the terrorists reveals that he knows you are in fact a CIA agent and kills you- setting up the course for the rest of the game.
2. D-Day - Medal of Honor: Frontline
Medal of Honor: Frontline has perhaps one of the greatest opening levels ever conceived in video game history. You are tasked with storming Omaha Beach and it is as epic as watching it on screen in Saving Private Ryan. You start off in your boat approaching the beach- only for it to be hit with an artillery shell forcing you into the water while seeing your fellow soldiers being shot at. The shells are exploding all around you as you reach the Captain who then tasks you with rescuing four pinned down comrades by shooting at the machine gun nests overlooking the beach. The whole level feels frantic with everything exploding around you- you really feel totally immersed in the level.