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)
I absolutely love Hamilton's Commonwealth universe! Pandora's Star then Judas Unchained, then the void trilogy followed up by The Abyss Beyond Dreams. I've read all of them 3 times and thinking of doing a 4th round soon!
I've also seen House of Suns mentioned here a few times. It gets my vote for the exploration of deep time due to the speed limits of causality.
I don't know what it is, but I struggle with both series that take place in the Commonwealth. Pandora's Star took quite a bit for me to get into, hooked me right as the book ended, but I enjoyed Judas Unchained after that.
I just finished Dreaming Void (Void #1), and it flowed the same as Pandora's Star to me, but I've grown a little over that kind of lead-up and then just end the book. On top of that, the world shifted too much, and it's hard for me to feel like I understand it in the slightest. I've been hesitant to continue it.