I've only ran HoL once just the other day to finish 3 quests (I haven't done heroic yet). I'm heroic geared and can down Gundrak, DTK, UK, CoS on heroic really fast and easy with no deaths, and I still found regular HoL a bit difficult - enough that I thought "Wow...on Heroic this would be insane". I will have to try it again though.