I'm surprised so many are having difficulty. I really found it rather easy on Hardcore. The Deathknight was 2Handed Slashing Melee weapon (usually an Axe but I would have preferred a sword for aesthetic reasons) and the hero was Crossbow with usually poison or explosive arrows. The DK also learnt Poison skill up to about half way. Everything went down easily, even the Earth Elementals. The only time I had problems was in the random teleport area when I'd port into 6 Earth Elementals. The only magic I used was individual Heal and act 3 onwards I never cast it again. If you want a tactic stick the Archer on aggresive and lead with the DK. Enemies target the DK becasse he's closer and the archer can pepper them while you move the DK around. Anyway 3 arrows or 2 axe blows killed most everything. Maybe you need to rearrange your skills a bit. Usually it's only cost effective to put 1 point into a weapon skill except for accuracy which needs 5 or so.
Yes, DK has a nice protection, it seems. It was a big mistake from my part to make him a magician, but I won't restart my game because of that <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />.
