I agree to all the points, especially the need for a story and focus on character/relations.
There are good sequels that totally leave all original characters and still work. 28 weeks later takes a new group of people, and brings new themes. The characters and story telling is very different, and still (IMO) it works. Deus Ex HR manages to stay close to the original but with a new set of characters and atoryline, and it raises more questions about todays society compaired to the original.
ESB vs ROTJ: there is a lot going on and a big story to tell in short time, so there were less time to focus on characters and relations. ESB has a more interesting characterization, but the story leaves more room for it. A problem ROTJ shares with the SW prequels. To much to tell.
I haven't played any of the Deus Ex games, so I can't comment there, but I can say that I was not impressed with 28 Weeks Later. I thought that the first film didn't need a sequel, really. It was a neat concept, executed competently, and that was that. I don't disagree with your underlying concept, though -- I do think that the themes/setting can be retained sometimes while a whole new group of characters is introduced....but I think it's VERY hard to do it well.
Re: the "Too much to tell" issue, I don't think that's ever an acceptable explanation as to why character development is ignored or given short shrift. There's always time to develop the characters...if you have their development be integral to the plot. I don't really think, either, that there's "too much to do" in ROTJ. I do think, however, that they tried to do too much. I'll explain.
At the end of ESB, you basically have three to four main things that need to happen: (1) Han has to be "resolved" (rescued or killed); (2) Luke needs to become a Jedi and complete his training; (3) Luke needs to "resolve" the issue with Vader (either killing him or getting him to give up); and (4) the Empire and Emperor need to fall.
The last three can all conveniently be stuck together, and are in this case. Luke must confront Vader, who is with the Emperor, who is the head of the Empire. Decapitate the Empire, and it will fall (so it's implied). So, the confrontation with Vader is also the confrontation with the Emperor, and thus is the keystone to knocking out the Empire.
The Han thing, I think, was never effectively dealt with, though, because it was so...minor. Why invest all these resources into getting Han instead of declaring him a casualty of war? They never, for example, effectively tied Jabba to the greater concern of the Empire...but they COULD have. The rescue mission could, by making Jabba involved with the Empire somehow, for example, have uncovered that the Emperor would be going to some location, which would force the final confrontation, etc., etc. This would mean that the story at the start of the movie neatly feeds into the overall story of the film instead of feeling like a totally separate issue.
The other problem is that they simply "embiggen" the rest of the elements. Not only must Luke confront Vader and the Emperor, but they have to blow up the NEW Death Star! And they have to launch a commando raid to do it!!! And they have to launch a space attack to do it, too!!! And they have to get the Ewoks to help them!!! So, already this goal of taking out the Empire is getting way more complicated. The pieces end up fitting together reasonably well, but they really just feel like set pieces instead of an organic whole. And they're recycled. Commando raid = rescue Leia from Death Star 1. Space attack = space attack on Death Star 1. Luke's duel with Vader = Luke's duel with Vader in the LAST film. All of that, I think, contributes to a very "busy but kind of not that thrilling" feeling with ROTJ. Plus, the Ewoks are lame.
Personally, I don't think ANYTHING or ANYONE can make a good prequel. I've come to hate the very concept of a prequel. If you're gonna tell a story start at the beginning.
I think it can be done if you only have a vague sense of "how we got here" or "what came before," but I think it's a LOT harder to make the audience care. It's like history, really. Even though you can know how it ends up, history can still be made interesting and exciting, especially if you only know the major points, and not the nuances of it.
For example, take the HBO series Rome. We know that Julius Caesar is going to die and, eventually, so will Brutus and Marc Antony, and Octavian will become Emperor. We don't, however, know how the story will be told or characterized, and we certainly don't know Titus Pullo or Lucious Vorenus and their roles in the larger story.
All that said, a BAD prequel is REALLY easy to make, when it's just a hodgepodge of the visuals and beats you liked from the original, without any real reason to give a damn. That's when, like history, it just devolves into "This happened, then that happend, and then this happened. The end." It's like when your history teacher just made you memorize dates, instead of giving you any sense of why this stuff matters and how it informs on today. Or why the human stories in history are moving and exciting, even if you know that, eventually, blah blah blah happened.
As for sequels, I think something that would benefit ALL sequels is if they were planned for IN ADVANCE. Plan out the story arc IN DETAIL and if the first movie is successful then STICK TO THE STORY ARC. Have a freaking beginning, middle and end.
I hate sequels that just tag another one for no good reason other than to make a buck which is pretty much MOST sequels.
Every once in a while a tagged on sequel winds up being decent or even good but most of them aren't just because the story was literally an afterthought.
That's my opinion anyway
I tend to agree. The sequel may be fun sometimes, but many times, if you don't build your original with a sequel in mind, and at least make it so that the original can easily dovetail into the sequel, it'll just feel like "BIGGER!! LOUDER!!! MORE!!!!!!" for no real purpose. And I'm talking where the stories themselves are conceived of as a whole broken into multiple parts, rather than "We have [actor] signed to a 3-picture deal."