I died twice before I was able to finish this one. It really tests your flexibility in using your skills.
You'll want to focus any mages first obviously, but then you should be DoT'ing all of the rest of the enemies. As you do this, keep an eye on your teammates' health and drop cures as needed.
If you draw aggro, kite them around the mast in the center of the arena, but try to stay close enough to your pet (Topaz carby) so it can pull hate back via AoEs.
Once you get the trash cleared out, the boss isn't too bad (even though I did have to kite him for the last half of his HP).
The mechanics of the fight aren't too complicated, just remember that the sooner you whittle down the numbers of enemies, the smoother the fight will go.