Ouch, I'm playing a barb too and didn't die on Belial although he was a lot harder than any other previous boss. I'm used to wow tactics though and the Belial fight was a cookie cutter WoW boss fight. Hit him 2-3 times, dodge the colored prompts, hit him a few more times, etc. With the barb I use Leap a lot and it helped a ton when dodging his attacks. Also using Earthquake on Belial was god-like. Drop the quake right next to him and then dodge attacks. That alone took him down 1/4 or so life each use. You can do it every 120s, so I think I got at least two in on him during the fight.
I use Leap and Ground Slam (or whatever it is called) when engaging large groups. Then I swing away with cleave. Cleave with the explosive AOE upon death rune is OP IMO.

