It was full of iconic set-pieces like the D-Day landings, and completely transformed shooter-multiplayer forever. The graphics were incredible for their time, and were touted as insanely realistic. Call of Duty 2 showed off the true power of the Xbox 360, as well as the potential of Xbox Live and online play. Call of Duty 2: The second CoD game came as, possibly, an even bigger revolution than the original.
That being said, the game hasn't aged particularly well, and you would be much better playing some of the later games on this list.
Call of Duty 1: The original Call of Duty released in 2003 and revolutionized, like Halo: Combat Evolved had done only a few years previously, the entire shooter genre. That was pretty great, but the rest of the game was a complete mess. As Treyarch's first effort, the campaign was nowhere near as good as Call of Duty 2 (honestly, it was terrible), but it did expand Call of Duty's multiplayer to introduce 24-player maps. CoD 3 launched as a rushed and unfinished experience that was, admittedly, visually impressive for its time. Call of Duty 3: As revolutionary as the original Call of Duty games were, there was one disappointment among them.
