Came here for the first time last night with a bunch of friends and had a great time. Going during the week was a bonus because it wasn't busy and got through all 6 of the Haunted Houses fairly quick. (During the week you can print a coupon for $5 off from the website, not valid the last weekend before Halloween)
My two favourites, The Asylum and The Darkness (I won't describe these as I wouldn't want to ruin it for anyone who hasn't been).
The "characters" did a fantastic job with their makeup all the better for scaring. If you're in a large group its best to go "explore" in pairs as its easier to get frightened.
My only criticism: While your waiting in line get rid of the club music and play something that follows the Halloween theme.