He's a tough one all right. If you're under him in level don't bother (heck maybe even get a level or two up on him). Use the health barrels in the area. There are 2-3. BLOCK or roll away when he fires his flame breath. Don't just sit there and try to go toe to toe like all the other missions prior to that one.
Actually, he owned me with my fire brawler, cause I was using the Ignition tree. And yeah, he's tough. Best thing to do is CC him constantly (via combos, if you're not a controller). Let your ally NPC fight the other mobs and just CC this boss a lot.