Hmmm, not as realistic as they would like you to believe.
This game is based on promotions, and those promotions can help you buy skills. Sounds ok right? No. There are not enough skills in the game to fill up the meters. Thats a big prob. Another problem is that all you have to do to get a promotion is just go through M16 qualifacation training enough times.
The missions are all choice based, so one minute I can be a Green Beret figting alongside rebels, and the next minute I can be just your basic 11B footslogging in sewer. It also does not matter what your rank is, you can be a MSG and be called a PFC on the first mission.
All in all, this game has many flaws in the military sense, but "okay" gameplay. I reccomned you rent it first.