Here’s a lesser example: Cocoon: The Return.
The first Cocoon film was light, but quite sweet and I liked it. The second film ruined it.
Do you think it’s significant that the Google Ads are pushing HOME DRUG TEST KITS ? 
For me, it was Highlander 2. The wierd, mystical beings that drove the first movie are revealed to be exiled space aliens who were fighting for the right to grow old and die. Way to ruin an interesting concept.
What on earth are you talking about?
I hadn’t thought of that, but YES, YES, a thousand times YES!!!
Disney’s direct to video sequels for their great animated musicals kind of sucked all the intimacy and allure out of those films: made them seem less like great works and more like the start of the latest franchise of ad naseum repeats.
I’ve seen all four Highlander films, & much of the TV series. The movies are bizarre, in that no two of the four are in continuity with each other. I think it’s even debatable whether IV is in continuity with the TV series.
IV is a ridiculous overstuffed mess. I hate III, consider it the textbook case of bad sequel/fanfic writing. II is just pathetically cheaply done.
But I still like the first one.
The Halloween sequels after number 2.
Halloween - great, Myers tries to kill Strode and only succeeds in wounding her by the end of the movie, the paramedics take her away, so what happens in the sequel?
He follows her to the hospital to finish the job! Perfect!
After that they just started adding incomprehensible crap about druids and that “thorns” as they tried to explain away Michael’s apparent indestructability. Really ruined Myers as a villain for me.
H20 wasn’t bad, largely because of the ending (which they undid in Resurrection, gar!), and the fact that they ignored all the druid nonsense from sequels 3-6.
Sort of in the same vein: mention anything about the Star Wars prequels and I will start crying and run to hide under a blanket.
More hate here for Star Wars prequels. I only saw Phantom Menance, and that was enough. Nothing I’ve heard from anyone else has made me want to see the rest of the prequels. Even PM was enough to bring my annoyance with things in the original Star Wars movies to new heights.
I don’t know what people are talking about with Highlander sequels. No one would be that stupid. What can you do after McCloud gains that power? He’s the one. What? You want to make him an alien or something? How cheesy would that be?
I also want to nominate the sequel to Mr. Roberts. I refuse to google for it, but it focuses on Jack Lemmon’s character and it is so painfully lame you forget he stood up to the captain at the end of the first movie.
See Revenge of the Sith. It’s great 80% of the time and when it sucks, it’s no where as bad as Phantom Menace. I only cringed one time.
[George Lucas falling to his knees]My… my movie was only good 80% of the time? NOOOOOOOOOOOO!!![/George Lucas falling to his knees]
Star Trek II made me enjoy Star Trek: TMP less, because the sequel was so good that the original’s flaws became even more obvious!
Yeah, to be fair, Revenge of the Sith wasn’t horrible at all, and could have served as a mediocre-to-good prequel all by itself. Even Return of the Jedi has its fair share of embarrassing parts. Sadly, the first two prequels are so gut-wrenchingly horrendous that the entire Star Wars franchise was tainted as a result.
Heh. Not what the OP had in mind, but quite true. The first Trek movie serves primarily as an example of what happens when you try to make a two-hour movie out of a one-hour episode 
I only got around to watching the final Matrix film last week, and right now, I’m considering rewriting the two sequels if I fall into unemployment. The first sequel could pretty much stand as is – I’d mostly cut a few scenes, especially the big fight – but the third movie needs drastic work.
I agree with Bryan though. It’s amazing that they can use the exact same shots in the sequel and make a far, far better film!
In retrospect, what the Star Wars prequel really ruin is Yoda.
[spoiler]Yoda’s great plan is to, get this, basically hide and then die in a swamp for NO REASON after attempting ONCE to do ONE THING to try and stop the continued rise and rule of the Sith. Oh yeah, and he’s going to learn to merge with the force, also for no apparent reason other than to pester people with visions and voices after he’s dead.
I mean seriously. How can he possibly complain that Luke is “too old” to begin the training in Empire, when it’s basically Yoda that decides what to do with the supertwins that could be the key to defeating the Sith (and he decides… to basically ignore the heck out of them)? I mean, I know that dying alone in a swamp SOUNDS like the best way to defeat the Sith, but wouldn’t training or working with the remaining Jedi as well as the children of the chosen one be a better long term plan?
Is this what previous Jedi did when faced with the Sith? Oh, we fought to a draw (and I seemed to have the upper hand until his guards came) once… so I’d better just give up for all time and allow them to control the galaxy. Ho hum.
[/spoiler]
Queen of the Damned, which sucked so badly I wanted to scream and throw things at the screen in the theater, which is not like me at all. Now Brad Pitt and Tom Cruise seem like brilliant actors by comparison. You think maybe that’s what they had in mind all along?
Don’t even get me started on The Passion of the Christ 2: Our Risen Lord Kicks Some Roman Ass, let alone Back to Casablanca: Weekend at Rick’s or even Citizen Kane 2: Rosebud’s Return.
Better that those movies had never been made at all…
I thought that Apollo 13 completely screwed up Apollos 1-12.
And you forgot to mention his lightsaber fight, which was such an obvious sop to fanboys that it detracted from the actual scene it was in.
I think it’s better to say “In retrospect, included amongst the many things the Star Wars prequels really ruin is Yoda.” Because I felt that despite Ewan McGregor’s actual, real acting - rather unique in the series - they also ruined Obi-Wan by making the entire thing his fault. If he isn’t so rude to Anakin all the time and trains him better, the whole Vader thing doesn’t happen. If he just finished Anakin off on Level 10 - I mean, the lava world - then none of it happens. Having learned how those things “really” went down, I’m left wondering why he didn’t spend all of Star Wars smacking his forehead and saying “man, I’m such a bonehead!” :smack: