(Please keep in mind this is only my opinion) The best ways to kill the big guys or as I call them, Void Brutes, is to punch them in the head it's a one-shot w h y. For the b o o m e r s (I guess you could call them suicide turrets) the best is pistol, shotgun or rocket. Spider thingies or void crawlers as I call them best weapon is probably rocket, pistol or shotgun. The sphere-shooty-thingy (I call them void turrets) probably pistol, your fist, shotgun or rocket. Also the rifle is literally only good when you freeze time.