Widow makes a mockery of most enemies. Scions, dead in two shots. Harbinger, mostly two shots. Most bosses, two shots (three if they have shiels, barriers and armour).
After playing a soldier in my first game, I felt very naked in my second game, when I no longer had an assault rifle. With the improved magazine capacity for the submachine gun, it makes and ok substitute for close combat. Sniper rifles are the preferred tools of trade for Gorth Shepard though.
When mobbed by husks, just punch them in the face and then incinerate them