What kinds of games are you playing? I've not found the list too unbalanced against standard Epic Arm. lists, but to caveat that I have only tried against Orks, we are both pretty inexperienced players of EA and have lists based entirely on how cool a miniature looks - I know with GW games this is always a recipe to lose..
I have read comments from tournament players who have said the HH lists are under-powered by comparison, but I couldn't say whether that is true or not.
Unit wise again I don't have much experience of standard AG to go against. HH I seem to have larger blocks of units - as you have the larger companies and then can end up with a bunch of support squads attached as well.
Fellblades seem pretty powerful as well, they made mince-meat of some ork units but then ran into a Gargant and got popped.
I have World Eaters who have a really nasty unit - Rampagers. Have extra attacks and are Berserk (can charge like Orks), also fearless - these totally destroyed ork units they hit in the games I played.
Destroyers seem a bit of a waste of time - we might house rule their guns to -2 modifier or something because they are expensive and just seemed to be crap.
Finally, it's quite cool having some of the artillery options - Basilisks being crewed by Marines. I can imagine these would be good but I haven't done a good job of protecting them in the games I've played.
So in summary, apologies my post isn't very useful at all, but I'd be interested in whether you find out anything about it!