Campaign: The Campaign is intense, interesting, and fun like you wouldn't believe. So many quotes and images that still carry today, like the crazy Kommandant and Sgt. Reznov. The American Campaign is hard, but rewarding. "Burn em' out" is one of my favorites. You get a great feel for the game, before even looking at the multiplayer. It's fast-paced, interesting, and good for any generation of CoD player.
Multiplayer: The multiplayer is a great start for anyone looking to get into Call of Duty or any FPS game. The microphone quality brings memories of shouting matches with randoms online for new players and hardened veterans. The unlockables put the new Call of Dutys to shame. Customization is small, but fruitfull. Gameplay is tight, it plays well, and you'll make many friends if you play long enough.
Zombies: This is the game where the "Zombies" game mode started. A classic in the Call of Duty series, these Zombies will scare you to death unless you're playing with the boys. It's fun and engaging.
Extras: Music and sound design is top notch. The music is blood-rushing intense, but also calmingly foreshadowing. Guns are well designed and fun to shoot with. The Achievements are hard, but it is exhaustingly proud to complete some.
I hope this review makes you buy the game. Please buy it. Now.