They are good only to clear your mind from time to time... (in my case in very rare occasions).
but horror without motifs, believable characters/actions, psychological
tension and atmosphere is nothing in my book. I m a great fan of atmosphere, strong acting,
psychological tension and therefore consider The Silence of the Lambs as one of the greatest
movies in that field. Of course when we speak about SF (horror) then we cant even start to speak
without mentioning Alien, The Thing, Videodrome, The Fly,...and many other movies (often older ones)
*P.S. Cameron's sequel to Alien is different in many fields from the original one.
Aliens is not a movie of atmosphere but it builds its tension upon action and
fast sequences. Its an action-horror/thriller, and one of the best in SF genre. Great sequel.