Single Player:
First let's focus a little bit on the quality of that game. Beside some minor issues a few users experienced, "Call of Duty" is a game you Buy -> Install -> Have fun with. Why do I mention that? Because this is nothing normal today. There was no Patch available right after the release. And yes, you can play through the whole game without the obvious need of a Patch, nearly unbelievable, is'nt it?!
That's something special today, because most games did not reach that level of quality and cost the players for that a lot of fun.
One aspect how this is achieved by the developer "Infinity Ward", is for sure that they use the Quake III engine. One might think that because of that the game might be look a little bit outdated, but that's definitely not the case.
What mostly all reviews in famous print magazines and on websites testify by their ratings, that the game is great, can only been repeated by me. But there is one thing I did not see mentioned anywhere and that's some small flaws when it comes to the difficulty balance. Let's make that clear from the beginning, I am no Shooter profi and I hate to use cheats or something similar to play through a game, but I am an experienced player. In the case of "Call of Duty" I was forced to Cheat my way through three of the overall 24 missions. These missions where Pegasus Day, Airfield and Pavlov. After several tries I still did not managed to get past these missions and at the same time I thaught that I could have choosen a higher difficulty setting for all other missions. So thats definitely something "Infinity Ward" should address in a future patch.
Beside that the only other aspect that gave me room for complaints, is the fact that the game is definitely too short. A experienced gamer will play through it in about 25-35 hours.
Compared to "Medal of Honor", "Call of Duty" is much more immersive and more focused on teamplay in the single player missions but on the other hand much shorter.
To finish this review let me say that this game is by far one of the most immersive games I ever played. Great Stuff!