My main class is Amazon, but i tried making a Barbarian and solo HC last ladder. It was more difficult than i would imagine. When you start running away from monsters to heal up, you start taking more hits, because your defense hits 0. It requires a bit of tactical thinking.
Bowzon is no cake walk either, you always have low Hit Points. You cannot rely on D/A/E to save you, although it may from time to time.
But the biggest trouble i have is with Necromancer. Very low HP, and relying on your Summons make you forget about being cautious. When there is a strong boss pack/Lightning/Cold Enchanted or any unusually strong as such, it may very well be the end of you. Once, i even had mid-decent gear, made it to Act 1 Hell, and died to a Cold Enchanted boss monster. I distinctly remember having 700-800 HP, while not having negative Cold Resists, but not much on the plus side either. I was shocked. It hit right on the outer edge of the ring too, i was pissed ^^