For me it is all about the world building, the practicalness of the universe presented. Dune had a decade of planning go into it before the first book was written. The rest did not have that amount of background effort and it shows. After the first book it all feels like he's making it up as he goes along, instead of drawing on an encyclopedia.
Children of Dune had the most egregious problem with this. Trying here to not spoil the plot for you, but at towards the end (page 329 of 408 in my edition) Leto discovers something profound. The backstory to introduce this was first mentioned on the previous page. It didn't use some bit of trivial from the first two books, and he couldn't be bothered to write it 300 pages earlier either. (Feel free to email me when you think you've reached that part.) The later novels are slightly better, then he's writing these new discoveries into the previous chapter.
Re-reading Dune has always been pleasurable for me. You can feel it is just the tip of an iceberg and tease out the history by reading between the lines. The other books lurch from one deus ex machina to another.
Ender's Game is also largely about consequences too. Humanity wins the fight and destroys the big bad, but this doesn't happen at the end of the book. There is still a third of the story left to mull over the consequences.
edit: Slight spoilers, but nearly all of the later Dune books essentially allow anyone to come back from the dead. He never once explores the ramifications of this. What happens if you try to bring back multiple copies of someone at once? Does every cell in our body really carry the full weight of our entire past experience? What about identical twins? What if you blended the nucleus of one person with the mitochondria of a second and the cellular plasma of a third?
Or does the procedure somehow tap into the soul? Is god annoyed that the natural cycle is broken? Does the process damage the soul? Never once delves into any of this, instead it is used only as a cop-out to avoid creating new characters.
I hear what you're saying. I'm gradually arriving at a model of "good book" that includes what a person's particular transgressions of suspensions of disbelief are, and what degree is required to trigger them.
For me, the biggest things are currently "must be at least this hard sci-fi" and "must have believably human characters." It sounds like one of yours is "must have book-spanning world-building." Which I get, but don't think bothers me as much.
I expect the unexplored deus ex machina will probably irk me when it shows up though! Though maybe not, I think a large part of my enjoyment of Dune is the somewhat orthagonal-to-Western world-building. Although the Islamic religious echoes are ham-fisted and shallow sometimes, it's still refreshing to even read something attempting it.
By my memory, Ender's didn't mull over consequences nearly as much as Speaker for the Dead, Xenocide, & Children of the Mind. It was more "Oh my god, this was horrible" and less "We did a horrible thing, so what do we do now? And how does that inform our reactions the next time we're presented with the same choice?"
Side note: if you ever want to read something laughably bad, especially for how modern it is, read one of the Honor Harrington books from David Weber. I tapped out after 20 pages.
Maybe world building is the wrong term? I consider civilizations, economics, infrastructure, etc, as another character in the story. They have background and develop over time. They should be as believable as the humans. This is common in the "future history" sub-genre but you find unexpected gems too. Discworld was remarkably good about it, for example.
Just found my copy of Ender's, one of the few OSC books I still have. I got the proportions very wrong. The story was "over" on page 295 of 324. So like 9%, the entire last chapter, was about the aftermath. Mostly Ender dealing with what happened. Still way more than the usual "happily ever after" and sequel hook you normally see, to give it credit.
The Honorverse is the purest of space opera. I have too many good memories to agree with you, but I won't push my luck with a re-reading. I seem to recall that it actually was pretty good at having their magic super weapons, drives and shields progress reasonably over the series. Weber was very good about having military tactics shift in step with the technology.
That's a more detailed way of putting what you're looking for. And I enjoy books like that as well (e.g. A Song of Ice of Fire). Incidentally, how'd you feel about KSR's Mars books, if you've read them?
But I guess I forced myself to read enough Golden Age sci-fi that I developed a neurotic category for lazy... "deep worlds"? I'm looking at you and Foundation, Asimov.
So much of that stuff is a splash of human-esque characters and plot on an otherwise naked thought puzzle that I feel like it deserves its own category. I suppose it irks me less when I feel like the author did that not because they couldn't do otherwise, but because they intentionally didn't care to. Which is to say, the thought puzzle interested them more than the characters.
I feel the same about Lost. JJ Abrams doesn't give a damn about solving mysteries. He just likes creating them. Not liking him for not solving them is like not liking a dog because it wags its tail. That's a valid preference against tail wagging... but maybe not dogs for such a person?
And I really wouldn't chance a reread. I started reading it because I'd heard good things about the tech. Let good memories lie.
The lines that did me in were something to the effect of: "{Someone does a thing that makes Honor happy}. Honor felt happy because someone did a thing." (!!!)
Mars was alright. I had a lot of trouble with one of the books. Took almost a year to read because it felt like there was nothing but political infighting in it.
Foundation was actually what got me started on the "future histories" kick. The civilization is a more fleshed-out character than any human in the story. But I was eleven and didn't read any further than the original trilogy.
My favorite golden-age sci-fi would probably be Heinlein's "The Past Through Tomorrow" collection. The parallels between Elon Musk and D. D. Harriman are amusing.
Children of Dune had the most egregious problem with this. Trying here to not spoil the plot for you, but at towards the end (page 329 of 408 in my edition) Leto discovers something profound. The backstory to introduce this was first mentioned on the previous page. It didn't use some bit of trivial from the first two books, and he couldn't be bothered to write it 300 pages earlier either. (Feel free to email me when you think you've reached that part.) The later novels are slightly better, then he's writing these new discoveries into the previous chapter.
Re-reading Dune has always been pleasurable for me. You can feel it is just the tip of an iceberg and tease out the history by reading between the lines. The other books lurch from one deus ex machina to another.
Ender's Game is also largely about consequences too. Humanity wins the fight and destroys the big bad, but this doesn't happen at the end of the book. There is still a third of the story left to mull over the consequences.
edit: Slight spoilers, but nearly all of the later Dune books essentially allow anyone to come back from the dead. He never once explores the ramifications of this. What happens if you try to bring back multiple copies of someone at once? Does every cell in our body really carry the full weight of our entire past experience? What about identical twins? What if you blended the nucleus of one person with the mitochondria of a second and the cellular plasma of a third? Or does the procedure somehow tap into the soul? Is god annoyed that the natural cycle is broken? Does the process damage the soul? Never once delves into any of this, instead it is used only as a cop-out to avoid creating new characters.