Shotguns are nice and all, the damage output is ridiculous. But that requires you to get up in the face of something. The reload speed can also leave much to be desired in PvE, since it's one shell at a time and not the whole magazine. I'd rather use a sniper, that can really reach out and mess something up before I'm even within their range of fire, or a fusion rifle that staggers all enemies and has fairly decent range and reload (enter my beloved Plan C that I've had since week one of the game)