The damage is amped up significantly in heroic, so for example the aoe he does every so often (30 seconds?) hits for something like 15k each in heroic vs 4k in normal, and the damage he does when people are spread out hits much, much more in heroic than regular.

but as said he is a very simple boss if you just stack up, have some heal streams (or group heals) going on, and do a mass heal right as he is casting his 3-sec superspell. No need to move or anything. Of course this fight would be much harder if you had a paladin healer for example.