I feel like I wrote this post from time to time on Reddit and I think I'll start this tradition here. I'm. a Honor Harrington fan. I've read several other space operas and they always fall short. The three that came close were Lt. Leary, Kris Longknife and Vorkosigan saga. Lt. Leary was nice, but it failed on World building. Kris Longknife also failed on world building and had astronomical levels of cringe with aliens and plot, but I enjoyed it. Vorkosigan saga had better world building and it was nice overall, but the books without Miles Vorkosigan weren't enjoyable. There were other series that I enjoyed: Serrano Legacy, Vatta's War (those are some of my favorites but they were too short), Starship's mage (it declines with every new book), The Lost Fleet (it has a serious plot problem, the plot doesn't move forward), Old Man's War (it was really nice), Dread Empire Fall (also awesome), Teixcalaan (good, but short), Alarm of War (good, but short and pretty generic), Bobbiverse (I read until book 3, it isn't for me), Red Rising 1st trilogy (really nice, but too Hunger Gamish, this whole dividing society into a cast system is getting old), Ark Royal. The Three Body Problem was awesome and, contrary to most series, didn't leave me craving more after it was over. Edit: forgot to mention The Expanse, it was OK.
I think that what won me over on HH was the fact that she is a complete Mary Sue and other character don't fall far from the tree, there is a nice world building, characters die, and there is a ton of action.
On the other hand, there are some long books that I enjoy that aren't space operas. I really enjoy the Dresden Files (because he is cool and it is a long series), I absolutely love Jack Reacher (it is just a nice fun read, it's like a nice Big Mac), I also enjoy The Spellmonger series, and I enjoyed the Riyria. I disliked Takeshi Kovacs (lack of sequence and plot) and I absolutely hate Southern Reach (VanderMeer), and there is another popular sci-fi book that is written as a report, which I also hated. I don't like those very innovative mystery stories where you are trying to figure out wtf is going on or waiting for a plot to start until the middle of the book.
Got any suggestions? =)
(OMG, after writing this post, I see myself as an incredible hard reader to please)
No love for Iain M Banks? The Culture series looks like it will tick all your boxes and instead of following a single protagonist the Culture itself is the protagonist so each book has it's own cast of interesting characters.
I second this. The Culture cycle is one of the best space opera series ever written.
I really enjoyed the Culture setting but had to give up after Look to Windward because that was about 3 books in a row with unsatisfying endings.
+1 - Banks is probably my favorite sci fi author (as you might have guessed based on my username). The Culture series is excellent and highly entertaining.