The accuracy of the weapons are similar to those of their real-life counterparts. If you run like a rabbit and go crazy with the akimbo berettas, you aren't gonna hit a lot of targets from 100 paces away. But if you kneel and zoom in on a poor sap with the sniper rifle, you can get kills from across the level. The realism factor also means that there are no magical plates of turkey legs on the floor that somehow repairs your wounds upon contact. Be prepared to die.
Some items naturally are unrealistic based on movies anyway.
But for gameplay purposes other things are tweaked even more. This is not Real Life Half-Life.