As an Iraq war combat veteran, I will say that Generation Kill is probably the onscreen depiction that comes closest to what I experienced.
The thing that almost no movies or shows get right, is that people get freaking weird when bullets start flying, even professional soldiers. Because despite all that training no one really knows how they will react when bullets start whizzing by them for the first time.
The grizzled Sergeant with 20 years in the service may freeze up, the hard-charging LT might start spraying wildly. And that high school drop-out Private who spends 300$ a weekend on booze and has never made over 30/40 on rifle qualification, suddenly becomes cool as a cucumber and starts dropping the enemy with snapshots at 200 meters.
Real gunfights are wildly, wildly unpredictable, chaotic, and sloppy. And Hollywood rarely gets that right.