As with most bosses make sure you have a high stability shield and just stay right on his left side. Wait out his attack strings then get a one or two hits in. Summon if you need to, but i didn't find it made much difference.
Yeah, I figured it was a matter of just learning the patterns properly. I have a preference for dodging, rather than standing strong with a shield, so I'll try that. It's just been a while since I've been so thoroughly smacked down by any baddie in this game. Even the first two bosses in the DLC area were pretty easy to read and dodge. Something about this one just seems to catch me every time.