Who owns mythology?
It's definitely wise policy to disregard sequels that might otherwise damage the original. I certainly am not letting "Prometheus" get anywhere near my memories of "Alien." I'm prepared to ram my spaceship into "Prometheus" to stop it, if necessary, but will gallantly warn Charlize Theron to get out of the way first. Someone should have warned her to stay out of that wretched movie.
I was always a bit dubious about the efforts to graft "Superman Returns" onto the first two Superman movies - which were originally conceived as one epic story - but what we ended up bordered on cinematic necrophilia. There is no way to get from the mature but cheerful Superman who put the American flag back on top of the White House at the end of "Superman II," and solemnly promised the President he'd never fall down on the job again, to the emo train wreck of "Superman Returns" - who abandoned both the world and the love of his life, after fathering an illegitimate son with her. No offense to Brandon Routh, because it's not his fault (although I thought he looked just a bit too youthful at the time) but Christopher Reeves' Superman was a man.
There were a couple of good ideas sprinkled through the "Matrix" sequels, although the good stuff was left unexplored while the bad was belabored at length. The idea of the Machines creating a sustainable world-illusion by making deliberate allowances for rebellion is interesting - the perfect system must allow for imperfection. But it really would have been better to leave it with Neo, now literally transformed into the God Out of the Machine, telling the enemies of humanity he would leave the next move up to them, and flying off into the digital stratosphere. What happened to his promise at the end of the first movie, that he was about to show the rest of captive humanity a world without borders and boundaries? What did all the people strolling around that crowded street think when he hung up the phone and flew away? The sequels just kind of ignore all that, so we can have more kung fu battles against an urban dystopia backdrop. And is it just me, or were the fight scenes in the sequels dull and repetitive, compared to the eye-popping action delivered by the original? I don't think it's just because the first "Matrix" had the advantage of surprise and originality, because I still feel that way when re-watching all three films today. I still want to rewind the video and re-watch the fight scenes in the first movie right away.