Does anybody know a good way to kill super mutants? Do they have any weaknesses?
With the Awareness perk, you can see your enemies' damage resistances. This is a vital perk, and usually one of the first three I get on any character.
From my copious playtime, I have noticed that very nearly if not actually all super mutants have lower energy resistance than physical resistance. Therefore, I always switch to my laser weapon when fighting them.
Super mutant mobs often have a suicider with them. If they do, kill him first. He'll run at you and explode a nuke, which you clearly do not want. If you shoot the arm holding the nuke, it will explode. This kills the suicider, and usually several of his friends. You don't need to crit the arm or cripple it, just hit it. I usually use a crit to do this, to make sure I hit it with the first shot before he gets any closer.
They also often have hounds. These hounds do a lot of damage in melee, but are usually lower level than the mutants, and comparatively easy to kill. Once you've killed any suiciders, kill the hounds.
After that, just start picking off whichever mutant you can kill next. You want to reduce the number shooting at you, as higher level mutants usually don't do that much more damage than lower level ones, but take much longer to kill.
Super mutants aren't very smart. They'll run to find you if you back off, which makes kiting them one at a time fairly easy.
They'll also group up in doors. This makes for a great opportunity to explode them. Since they're weak to energy, this is a good time to use those Molotovs and pulse grenades.
Super mutants have fairly high damage resistance compared to most enemy types, especially the more advanced ones like masters, so spike damage is good. You want to use things like explosives and plasma rifles, not miniguns or pipe pistols.