I feel like its an action enhanced exaggeration of real life. Everything we do in CoD is possible and does happen in real life but in order to increase the excitement factor of the game there needs to be a boost in action, which sorta throws away some of the realism.
There are other games that are a closer resemblance to real life warfare but they lack excitement and fast paced action, which are two qualities that made the CoD franchise as successful as it is today.