You are not doing it right if you are SOL when you need 2 shots. When doing solo PVE I own anything before it gets near.
In co-op mode, I have to use both sniper and shotgun, I normally take my time and get headshots/crits. I can stay on the other side of a door and own the back of a bosses head while the others are running and gunning.
When you are facing down groups of 3 or 4 enemies it makes a huge difference if they take 2 hits instead of 1 to the head.
I guess it matters that I have the cloak, and after I kill 2 or 3 monsters/mutants I cloak and get my distance back. Or I use a bio nade and stick them to the ground while I blow their heads off.
But this is why some people snipe and some people don't, of course I've had bad luck in PVP with sniping. If you don't get a 2shot kill then you are kinda ****ed cause they will turn and own you before you can do anything unless you cloak and run away.
I don't have a lot of high level play experience with the game, I just played for a few hours in the beta and started as a survivalist. The pistol is total garbage, it seems to do no damage beyond maybe 10 meters, and the sniper rifle is incredibly good against everything I can one shot, but a serious liability against enemies that have no obvious weakspots or so much health that they facetank your rifle.
I don't have anything like bio grenades yet, I just have my sniper rifle and my decoy ability. I'm not doing bad by any means, but big enemies are a pain to deal with.
Where do you shoot a hellbug to do headshot damage? Does it have a critical location?