Call of Duty is very different from modern Call of Duty games. It doesn't have regenerating health, it has a different game engine, combat flows differently, and you are a regular soldier, not a super soldier or super agent.
The campaign follows three nations battle against the Third Reich and their constantly growing military. You play as Americans, British and Russian soldiers in different battles against different groups of the massive Nazi Army. As the American solider, you are fighting in France in a desperate battle to claim land and villages from the Nazi's, as the British, you go from standard soldier to SAS agent, and as a Russian soldier, you start as a lowly conscript and end as a senior soldier. In the campaign, you never feel invincible, and unlike modern Call of Duty games, you will almost always have a large amount of soldiers with you, rather than going alone or with a single invincible commanding officer. This doesn't make the game easier however, the lack of regenerating health means that it is unwise to carelessly move, especially on higher difficulties where having low health and no health kits for another mile can make the games campaign brutally difficult.
The soundtrack is a high-point for the game as well, with memorable themes. The voice acting is far from modern Call of Duty's Hollywood voice acting, but then again, it can stand with it as an equal because nearly all the Call of Duty games have bad voice acting (minus Kevin Spacey, he was the best part of Advanced Warfare of course!). The sound effects hold up to players because they were re-used for several more games, and as they stand, they aren't exactly low-quality.
Visually, the game has aged since release, with odd faces, bad animations and low-resolution environment textures. The gun models are noticeably lower detail compared to Call of Duty 2's models as well. Despite this, the visuals only get in the way if you decide to only focus on them. The engine is clearly quite old, but the game runs well on modern computers for most of the time. The only real annoyance is the lack of support for most resolutions, meaning that .cfg configurations are needed to run in resolutions such as 1920x1080.
Despite its problems, Call of Duty still stands as one of the best in the series, the game may be visually aged, it may lack the narrative focus of later games, but it stands taller because it focuses more on spectacular battles and large set pieces instead of plot and the excessive use of QTE's. I ultimately recommend this game to anyone who loves Call of Duty to see how the series should be done, and lovers of the genre as Call of Duty, and its expansion pack, United Offensive make the best the series. A stellar game, and a brilliant starting point for a series that has unfortunately lost its way.