Characters were about 16-17, who had completed the normal difficulty. Yeah, it does get nasty, since you're facing about the same number of monsters per area that are in normal. Even with some high-level summoned critters, it isn't very easy. Of course, if it were easy, it wouldn't be HOF
Also keep in mind that they do far more damage than usual. Youpr party can go down quite fast, given that armor class isn't all that helpful.
Nightowl2