As close to real war as you'd want to be.
The game starts off with one of the best sequences in any game to get you familiarized with the controls. Instead of sending you through a training course like the first one did, you learn how to shoot, move, and throw grenades in the back streets of war-torn Russia, using potatoes as grenades.
The game kicks right into the action, starting with the Russian campaign. You go through about 9 missions in the Russian campaign, broken up into 3 different segments. This includes hunting down German tanks through the bombed-out buildings, taking a train station and repelling a German counter-attack, and (the best sequence in the game), sneaking through an oil pipe to get behind the enemy and take them out.
The game then goes to the British campaign which starts you out in El Alamein and battles around it. In the British segment you also get to drive a tank as part of a company. The tank missions are, sadly, too short, but the other British missions make-up for it. You end the British campaign after 3 segments, but come back to it later for one quick segment in Caen, in France.
The last campaign is the American one. In the first game, you parachuted into Normandy the night before D-Day. This time, you start out in an amphibious landing, but it's not Omaha Beach. The American Rangers are tasked with taking out the guns atop Pointe du Hoc that are firing on Omaha Beach, and you have to scale a cliff wall while being fired at to make it to the top. The American campaign takes you through the Normandy country-side, and you'll get into some firefights that look familiar to the game Brothers in Arms, but Call of Duty does it so well, it doesn't like you're playing the same game. You then take control of "Hill 400" and have to survive an intense attack by the germans. The last mission takes you across the Rhine river, into Germany, where you are tasked with taking a town under heavy German occupation.
Every mission in the game is memorable, and very intense. The sound effects are great, especially the ambiance of battles taking place elsewhere. The musical score is some of the best classical/war music in any game.
To sum it all up, if you liked Call of Duty, buy this game. If you like World War 2, buy this game. If you like shooters, buy this game.