Call of Duty does a good job of providing a number of different styles of play and locations, but sometimes less is more. You fight against the Nazis as a Soviet, Brit and American, so unlike Halo2, you're always the "good" guys. You play as a sniper, tank commander, light recon soldier and regular ol' grunt, so you get a lot of different experiences. The historical research to keep it accurate is nice, along with the interviews during the credits. My two biggest problems with the game: 1) the AI soldiers working with you tend to get in the way more than anything. You don't control them like many games, so they step into your line of fire and sometimes even get in your way when you run for cover. 2) spreading the game out over three continents kind of short-changes each one. Just as you get into liberating Stalingrad or fighting the Afrika Corps or making the final push into Germany, that section of the game ends.
All in all, I'd say it's a good game, certainly worth renting. But I'm not going to run out and buy a copy of it. Good thing GameFly exists.