Greetings!
In the main game version You pretty much position your guys and they react on their own, as per Basic US Army standards/tactics etc (so they say).
You can get them to "bound" into locations, use suppressive fire into an area, use smoke and frag grenades etc. They take cover, and let you know when they are in trouble, and need to be moved...they also can be suppressed by enemy fire.
So it isn't a first person shooter per say, but more of a game of "tactical placement". You get 2 squads to operate, (Alpha, and Bravo) with an occational special unit... (aka Charlie) to operate, like for example an engineer that needs to be brought to some missles to disarm, or my fav' mission two Ranger snipers that can shoot around the enemies cover (if they aren't suppressed).
If one of your guys gets wounded you have to aid them, and get them back to a medic ASAP.
Loose two guys wounded or one dead, and it's game over, and you have to restart the mission.
So if you don't use these squads to support each other you will be in trouble pretty darn quick.
Unlike most AI Tangos these ones are often pretty clever, and fall back, regroup, find cover, try to flank, and also send RPG fire at you when they can nail your guys with an area blast. Some seem to be in fixed positions, but I'm sure online play will add enogh chaos to fix this.
The bonus US Army trainer on the X-box versions disk lets you get much more detailed, and select fire sections for each soldier, but has no extra unit to control (from what I have seen so far). I noticed tonight this version also lets you enter buildings, and clear rooms...secure fallen enemy weapons, and wounded troops, and allows you to camera pan the whole area at anytime of the battle, for replay, reflection of tactics etc...more of a trainer then a game.
Worth a rent before you buy IMHO.
http://www.fullspectrumwarrior.com/
Cheers!
R.