Typically Hunter Pleasure shows are judging a horse that goes quietly under english tack, with nice gaits (whatever is acceptable for that breed), and a general "pleasure" to ride in picture.
HUS locally is like the hack class after your over fences classes at a hunter show and should be judged in the same manner. Like Maura said it's judged on movement and suitability of a horse in the hunt field. Well it's supposed to be anyways.
OP- this is a class that will judge more in favorably of a forward moving, quiet, obedient horse, who is designed to jump. Another difference is you may be asked for a hand gallop. Is there an opportunity to watch this show or a similar one before going? That's what I usually try to do with an unknown event.