hi warrenss2,
from my experience of playing, a game takes 30 minutes to about an hour usually,
the gaming mechanics are pretty straightforward, roll anumber of D6 and compare highest, exceed a target number to do damage.
an 8 year old should be able to play easily enough, the only trouble we had at first was with armoured creatures attacked with armour poercing weapons, otherwise easy.
It can be used for all types of horror, most of the included stats cover very 'cthulhu-y' monsters, but there are the usual suspects too, mummies, zombies, frankenstein style monsters etc.
we usually play with from 3-7 or so miniatures per player, the mechanics don't seem to suffer and the game doesn't really slow down as each player only gets a certain number of activations each turn (2 usually plus any from leader types wit special abilities)
I don't really think there is an upper limit, i can see larger games happening in future with maybe 20 or so figures a side, this would only increase playing time
to maybe 1 1/2 hours or so per game.
try them, you'll like em.
regards
jim