The Matrix: When the agents have captured Morpheus, and one of them asks the other ones to leave, I was 100% convinced that the revelation was going to be that the Matrix was trying to follow a version of the laws of robotics, and was programmed to make humanity happy. Which it initially did by making a world where people could be happy in suspended animation. But parts of the matrix itself realized that the artificial world it had created wasn’t, in the long run, making people happy, so it was having a personality conflict, which is why all of the gaping security holes existed, and Agent Smith wanted to help Morpheus and Neo. Which would obviate the need for that totally idiotic battery explanation. Not to mention the second and third movies
Harry Potter: Given the meeting with the muggle prime minister, and given that one of the recurring themes of the book was Voldemort’s hatred of, and dismissal of, muggles, I was anticipating that the climax of the book would involve a scene where Harry had successfully gotten rid of all the horcruxes, and is facing Voldemort, but of course Voldemort is a vastly more powerful wizard than him. But a mortal one. And then, bam, a special forces sniper blows his head off from 1500 yards.
Buffy: [spoiler]Not a specific change, but one big that always bugged me about the series was how utterly idiotically inept and pointless the Watcher’s Council was. I mean, nothing about it made any sense. Basically every single thing it ever did (with the exception of hiring Giles, I guess) backfired horribly. It was exaggerated beuracratic infighting and inefficiency taken to the extreme.
Part of it, of course, is the idea that there’s only one slayer in the whole world at a given time. Sure, Sunnydale has a hellmouth, but given how many vampires Buffy has to slay ALL THE TIME, not to mention the other schemes she’s constantly foiling, how is it that every other place in the entire world has not been overrun long ago?
Further, there’s some inane dialog involving Kendra in which she says that in her village, being a slayer is taken seriously, or something. How can that be? There’s an average of one slayer IN THE ENTIRE WORLD every 3 years or so. So there should be one in her village maybe every other millenium?
The whole thing just doesn’t make much sense.
[/spoiler]