One of the worst sequels of all time

Rating: 2/10 (4 June 2012)

Anticipating the release of Prometheus, I decided to watch some of the alien movies again to refresh my memory, specially after I learned that the story would include the mysterious alien figure known as the "Space Jockey". Watching Ridley Scott's movie went just as expected, I continue to see it as one of the best sci-fi movies ever produced. The next day was James Cameron day and it struck me that there was a time when I considered Aliens to be a good movie, but now I find it just terrible. It rivals "Beneath the Planet of the Apes" as one of the worst sequels of all time.
*** Spoilers for "Alien" and "Aliens" from here on *** I'll just comment on some of the major points that made me reevaluate my position.
1.) The science: the Alien movies are not usually remembered by their scientific accuracy, nevertheless the few points that are made in that sense in the first movie are credible enough, and the lack of any further elaboration on controversial topics leaves the viewer free to interpret it in a convincing way. For instance we are told that Nostromo's voyage is interrupted when they are still months from reaching Earth, but it could be ship's time (see relativity). There is no communication with Earth, as one would expect if they were at a different stellar system. The fact that nobody mentions any family relation contributes to the view that work in space involves being away for long periods of time. But all that is destroyed by "Aliens" when out of the blue we learn that Ripley has a daughter, who is now dead, and that Ripley planned to be home for her 11th birthday. Aliens is full of scientific illiteracy like the fusion reactor that blows up if not cooled just like a fission reactor, and the orbiting spacecraft that just falls to ground when released by another orbiting spacecraft.
2.) Stupid military force: this is the element that proves the complete change of direction that the movie had taken. From sci-fi horror to almost a slap-stick comedy. An elite unit that resembles a bunch of teenagers going to a party, an irresponsible and inexperienced lieutenant that freaks out when half his crew dies, and a hysterical soldier that punctuates every sentence with "man".
3.) "They are on the ceiling!": in a highly sophisticated structure built in a hostile environment there is always room for the silliest plot device in the movie. While barricading themselves in the control room they forgot that the ceiling was completely open, even after Ripley specifically tells them to check every ventilation access, electrical tube, etc. That was the smartest thing they could think of to kill some more characters and keep them running?
To wrap it all up there is a reprise of the last act of the first movie, with the alien queen sneaking into the ship and being blown away through the airlock, intertwined with a pathetic mechanical suit fight and the worst line in the whole script: "Leave her alone, you bitch!"