Although there is actually nothing in the form of a coherent plot in Call of Duty, I gather that it contains some very crucial events from World War II history - events that actually took place. While that is cool in itself, the plot doesn't come across as too friendly occasionally bouncing from one timeline to the other. And as if this were not enough, the game makes you play as three protagonists from the American, British and Russian armies all launching different sorts of assaults on the German army (which can loosely be termed as the antagonist here). While playing as multiple protagonists is cool from a gameplay perspective since it offers you different views on sometimes overlapping situations (one such novel instance was in the end when the Russian soldier talks of meeting a fellow American "brother"), it doesn't help you identify and connect with any of the characters. It thus boils down to the other essential of gaming - gameplay.
Gameplay in Call of Duty is very fluid - especially the shooting mechanism. You can shoot using the cross-hairs as in other shooters like Half-Life but the game offers another shooting mechanism called Iron Sights. Right clicking the mouse allows for more accurate aiming as the gun zooms over the screen. Its as if you're aiming with one eye shut and looking right through the gun's aiming mechanism. From what I gather, Call of Duty pioneered the Iron-Sight mechanism that is now so common in other shooters. In addition to the shooting, the missions are highly varying from the typical run and shoot ones to some stealthy ones in Russia, to holding out armies of enemies until re-enforcements arrive (and these missions can be quite a pain on higher difficulties), to shoot-while-you're-in-a-vehicle missions. There are also two missions where you ride tanks and fire through them. You can run (default), crouch and prone (lie down) during the missions. The missions are short, tight and never drag on unnecessarily with some being even as short as 10 minutes in length. Although this makes the campaign shorter, it at least keeps the gameplay fresh throughout.
Since there are three campaigns in effect, we have three sets of weapons for each. That's the game's way of introducing new weapons. There's the Thompson and the Sniper rifle in the American campaign with their equivalents in the British and Russian ones. There are also grenades, pistols (not very much required), shotgun-types (although not true shotguns), MP-40s, MP-44 and so on. Also, in case you run out of ammo, you can press a button to perform a melee attack with the gun. Mostly though, there's enough ammo in the game so you rarely run out of it.
The game is presented through diary notes, instruction pages and the likes handed out to the game's protagonists. That's possibly the only game mechanic to contribute to the story. Plus, whenever there's a campaign switch (from the American to the British), a photographic reel with real images plays out which adds some authenticity to the game. Animations are again fluid, especially the iron-sight and crouching and proning ones which are mainly the ones that matter. Graphics, while somewhat dated, look pretty decent for a 2003 game.
Speaking of graphics, a lot has been said about Call of Duty's consistently 60 frames-per-second performance. Well, it certainly was true in my case - the game ran at 60 FPS at all times even at the highest settings. Perhaps that's because my machine is too recent to allow for a performance lag. I suppose a game like Black Ops would be a better game to comment on this aspect of the series.
There's very little music but there's one theme that plays in the game's menu and is also interspersed throughout the campaign and the ending while also playing in full during the credits. It seems to be the main theme of the game and is really a good piece of music conveying effectively the tragedy that war really is. Other sound effects abound with a huge variety of gun sounds, tank shots, explosions, human voice-overs and all are done incredibly well. With as many as four or five machine guns being fired simultaneously, it can get really noisy at times.
Its a shame that I can't really comment much on the multiplayer aspect of this game which is what the series is now known for since I couldn't find any servers at the moment (maybe they're all taken down or maybe its due to the timezone difference). And since I played this game directly on the Veteran difficulty, there's not much left in terms of value (after playing at Veteran there's no point in playing at lower difficulties). Some missions at the Veteran level can be incredibly frustrating. Examples include the penultimate moments of Pavlov's House when you have to hold enemies for 5 minutes till reinforcements arrive while enemies keep swarming at rates of half a dozen and the second Pegasus Bridge mission where again you have to hold off forces till reinforcements arrive. Both missions also include tanks to save yourself from which makes matters only worse.
Call of Duty has infamously become synonymous with glorifying war. However, my experience with it was quite the opposite - it actually made me realize that war is horrible. Perhaps playing it on the Veteran difficulty was what did the trick. Although there are quick saves in the game, in war its just one load. You die, the game ends, there's no reloading ever. With that said, Call of Duty is an excellent game with strong gameplay as its forte. Its definitely worth playing the one that re-initiated the FPS mania !!!