In the case of the movies I mentioned, its not just a plot twist or a new direction but a lack of quality acting, writing, director etc. Sure T3 has some good action scenes but does it measure up next to T2, no. That isn't hard for any adult to see. The Godfather series is a classic example of this.
What sequels can you think of ?
Anyone who can think of good sequels post them please.
There are multiple threads about sequels that are as good, almost as good, or better than the original film, but I will list a couple here:
Aliens - Although the first film is my personal favorite, most folks seems to like Aliens the best. It is certainly a fantastic film, and regarded as one of the better action sci-fi films ever made by many.
X2 - This one is better in almost every way than the original, IMO.
The Empire Strikes Back - Again, I like the first Star Wars the best, but this one is considered to be the most well directed film of the bunch, and also the more dark and operatic film, as well.
T2 - I notice you skip over comparing T2 to the original, while lambasting the third film (rightfully so, IMO).
T2 another example of a general consensus I have noted in that it outshines the original. I disagree, personally, as I like the gritty tech-noir feel of the first, but T2 is clearly well liked, and is considered to be a groundbreaking film. It is certainly well liked.
Star Trek II: The Wrath of Khan - The director's cut of
Star Trek:The Motion Picture made it a much better, more concise, and better paced film, but Star Trek II is still much better.
A Shot in the Dark - Not a direct sequel to
The Pink Panther, but it is the second Clousou picture, and I think you would be hard pressed tyo find someone that likes the first film more than this one. Superior in almost every way. One of my favorite Sellers films.
The Good, The Bad, and the Ugly - The best of the trilogy, hands down, and it's the third film in the series.
The Road Warrior - I certainly like the second film more than the first.
Bride of Frankenstein - Hard to top the first film, but alas, this does it.
Clear and Present Danger - A loose sequel to, and better film than Patriot Games.
Exorcist III : Legion - This is one of my favorite suspense/horror flicks of all time. I won't say it is better then the original, because it probably isn't, but it is DAMN good. This is a great set of films for this topic, because
The Heretic is quite possibly one of the worst films I have ever seen, but it in no way tarnishes the first film, nor the third, IMO.
Evil Dead II : Dead by Dawn - Half sequel, half remake, it is the definitive Evil Dead film.
The Dark Knight - The most recent Batman film is the best of the bunch.
So no - sequels don't ruin the originals in many, many cases, IMO.