I too have often wondered who decides to make so many sequels, not just to movies, but to everything.
Sometimes, they work out. I liked "Toy Story 2" and "Santa Clause 2". Whoever mentioned Disney sequels, though, probably nailed it head on. I've never watched the sequels and have no intention of doing so. For one thing, some of the Disney movies (Cinderella, for example) were based on fairy tales that existed for centuries before the actual movie. Another thing is that when they attempt to remake an older one, the voice actors have either retired or died, and most of the animators are gone as well. I don't know if they've attempted a sequel to "Pinnochio" but if they do I'll be upset, as it is one of my favorite movies of all time and everyone who worked on it circa 1940 is now dead, including Cliff Edwards (the guy who voiced Jiminy Cricket). When I saw a TV promo for another movie sequel, "Little Mermaid 2" (keep in mind I know and love the original--I saw it back in 1989 in the THEATER when it came out!) I was dumbfounded. How could you take an adapted fairy tale that already had a different ending than the original (Ariel dies in the real tale, I read it once) and then come up with a new plot that is nowhere near what the old guys from Europe did back in the day?
I can't say much about the Bat Man, Spider Man, and Super Man sequels you guys talk about. Aside from a few random episodes of Bat Man, I haven't seen any of this stuff really. I preferred to play baseball or soccer on Saturday mornings when I was little, so I didn't really know about or watch most of this stuff. I got educated in this stuff in kindergarten only after a lot of teasing--but hey, I could hit a ball further than the rest of them, so it was just what I liked, I guess. People I know who watch that sort of film have said the sequels are never as good as the first ones. I take their word for it, too.
The biggest sequel in theaters now is "Pirates of the Carribean". I heard the second one isn't as good as the first one, which I happened to really like, but I'm hesitant about the new one. I'm waiting for the DVD.
Then there are other things that get sequels. Books, for example. When I was a little kid, one of my favorite books was "Charlie and the Great Glass Elevator". After I had read it in kindergarten, my teacher told me that I should read the one that came before it too. There is an example of a sequel so good that you don't even need to read the first book to understand it.
Usually books are good if you have several sequels to them, but this is often intentional. I write, and I am already writing a sequel to my first novel. I think books work out better than movies most of the time as far as sequels go.
Then there are video games. Most of you folks on this board know a lot about them. Of the games I've played (the list is short, trust me) I know there are some sequels. For example, Super Mario 64, I think, has a sequel of sorts on the Game Cube. I saw it on display once but it looked pretty hard--you had to shoot some hose at the people. I can barely handle one control stick, let alone two! And the Mario Kart game for the Nintendo 64 had its sequel, Double Dash, on the Game Cube. I find the sequel to have more stuff in it, but I find it about ten times harder! I joined this board to try to beat the game, since I've had it almost three years now and I still have a lot of stuff left to go (at least I think I do). Of the other games I have, there are sequels to every one of them that aren't really sequels at all, but just updates. Other than Mario 64 and the Mario Kart games I have several different years worth of Madden and various baseball games (Triple Play, All Star, and MLB, depending on which one they decided to make that year).
Finally, there's TV. I don't know how many Big Brothers we've had now, or how many Survivors, but I think reality shows are so 2000 anyway. I'm more into talent shows like "America's Got Talent" or "American Idol" right now, and I've always liked game shows unless they're really lousy. And there aren't very many good sit-coms on either. I sure miss the days of "Fraiser" and "Everybody Loves Raymond", though "Two and a Half Men" is usually pretty good. Anyway, I'm ranting here. From the folks I know who do like reality TV and watch the numbered Big Brothers and Amazing Races and whatnot they say the sequels are usually as good as the original and they often add new twists.
I've come to the following conclusions about sequels:
1. Movie sequels are hit or miss. Often they work. Sometimes they don't.
2. Book sequels are generally good, but usually happen in a series.
3. Video game sequels just get too hard anymore. Game Cube is definitely my last video game computer, since I find it almost too hard! Nintendo 64 was easier! I'm only going to be 20 this year so I don't think it's my reflexes slowing down or something (and if it was, I probably would have had a horrible season in baseball last spring and I most certainly did not!)
4. TV sequels don't happen much but are usually okay.