Well what I think is so special about HH is the big events that turned the whole around, like battle for Prospero, Calth, Issvaan. They arent 40k where a whole subsector in war doesnt affect on the greater scheme. Thats why Nemesis isnt so highly fond of (I think its ok but pretty meeh, not contributing much).
I would want greater insight on the Legions, Primarchs and ect ect. But I want big turning events with that also, not a random story how a Primarch came to battle on a planet and then leave when he's doen.