No particular order:
Cold, Blind Terror -- will never forget a lone scare-actor, in a barely decorated room, just pointing to the exit as wolves howled on the soundtrack
Blood Ruins -- I can't even remember much about this one, other than being disappointed after every walk-through; first of a few underwhelming colonial houses (Foresaken, Roanoke), that era just seems hard to make work
P&T New'kd Vegas -- when a 3-D house works better with the glasses off, it's a problem. When the jokes would've felt dated in an 1982 episode of The Love Boat, it's a problem. And that over-hyped ending completely under-delivered. Was a huge P&T fan, so disappointment probably clouds my judgment, but the only room I thought captured their "vibe" was the Seigfreid & Roy one (SARMOTI!!!)
Fear Factor -- Just lame.
Reflections of Fear -- another one where being overhyped probably hurt an otherwise mediocre house. Was the icon house, should've been better. Friday the 13th, also in Jaws queue, could have taken this slot as well.
Tho I had an odd personal affinity for it, surprised no one brought up People Under the Stairs yet. I thought conventional wisdom had it pegged as worst ever.