At number 4 comes World at War, the first game in Black Ops series. The game brought World War II setting back to Call of Duty. It is considered to be the fifth mainstream game of the series. The game introduced co-operative mode to the series.
The game's story is told from the perspectives of a US Navy Officer and a Red Army soldier and is based on many historical battles. It was praised by critics and praised by players. The realistic combat and good graphics along with a nice story earns it the fourth spot on this list. Also, those Nazi Zombies maps that you love, World at War is to be thanked for that.