They'll tear you up if you're a melee class, or else have to rely on a melee companion. For instance, I can get around them on my Sentinel by using Rusk or Doc instead of Kira, T7 or Scourge (T7 works if I remember to turn his jet boost off too, but I rarely do that). Otherwise it's a frantic race to destroy the mob before I get wrecked by elemental damage that I can in no way mitigate outside of Rebuke/Guarded by the Force.
But my Sentinel can self heal, and with practice I've learned where to stand to maximize the space I have available in melee range. My Jugg it's harder. I have to run with Vette or Quinn, as there's no real use using Pierce for ranged damage over Vette, and Broonmark will just get owned by the aoe, as will Jaesa. Now, it took me about 45 levels, but I eventually learned the position maximizing skill I mentioned a moment ago. This works...most of the time versus ranged mobs that use this skill. Melee mobs are far easier, since you can just drag them out of it, while ranged ones will just sit there and keep firing on you. So unless I can nail the positioning just right, then I get one chance to reset with Push, which more often than not is enough, assuming it's safe enough to push them in the area (i.e. other stuff won't add).
It's not game-breakingly hard, but it's something that turns "pleasantly challenging" into "pure @#%^ing annoyance." The same goes for any kind of DoT-using mob. One DoT isn't a problem, and two isn't too hard to deal with, but any more than that and I find my admittedly well-geared Juggernaut suddenly at critical health. I get it, elemental and internal damage ignore armor/defense/shield etc., but the balance is that these kinds of skills are supposed to be rare in some way. The few mobs that have both this damnable little turret and more than two DoT's are just ridiculous to face as a non-healing class.
The thing about me is that apparently it's very hard to tell when I'm drunk. So I feel like I'm walking sideways on a UFO and everyone else sees me doing the robot like a pro.
i have bathed in the blood of many. my life was spent well.
feral druids do it on all fours.
The One True Prophet of Tonkism. http://therewillbebrawl.com/