Both of these franchises should have never gone past their first movie, IMO.
"Alien" was a great movie. Way ahead of its time with the effects and creature creation. H.R. Geiger's alien design is a work of art as far as I am concerned. Good story, but no need for it to continue.
"Predator" was okay. Again, some nice effects work with the cloaking device. It really didn't call for any continuation of the storyline by a sequel, though.
Some sequels are fine. They make a logical continuation of the story from the previous film (or at least attempt to most of the time). Dragging out a "cash cow" for movie after movie is a waste.
on principle I would have to disagree, while predator 2 was not a very good movie, the first one was excellent, especially that last half hour or so, and the sequel to alien, aliens, is a fantastic movie. Sure 3, and resurrection were not particularly great, but to say sequels are only logical if they continue the story of a previous films would be false, many successful, and well executed sequels break new ground, and take characters in new directions.
films like the good the bad and the ugly, Aliens, the wrath of Khan, from russia with love would never have been made
even films like raiders of the lost ark and a new hope a worlds apart from their sequels (and imagine having a single star wars)
No, i think AVP-R may not be the greatest idea, but if ridley scott or james cameron were to take on another alien film, that would be very good news