You reload in previous games, but its not a gameplay mechanic. This time, on the right of the sight reticle, there is a meter that keeps track of how many bullets are in your weapons chamber. After you fire them all, it goes to red, and you have to wait a few seconds for it to reload.
Traditionally in Earth Defense Force games, you are running-and-gunning the entire time. Throughout the maps there are crates with ammo and armor to restock. In Iron Rain, however, you have a limited number of shots for your primary and secondary weapon. You must be more careful with your firepower, changing how you approach the insect onslaught.
Since you cant fire your weapon while its reloading, it becomes necessary to get away from the giant bugs, who seem more intent than ever on finding you and killing you. They are the most relentless bugs in any EDF game to date, willing to climb up and over buildings to hunt your ass down.