I've always enjoyed books that put effort into creating a believable world that has fiction mixed with fact. Sometimes that's Science-Fiction with the specifics of military or chemical reactions or theories. Sometimes I just want a good crime fiction that is believable and paints the setting in the way it looks in real life.
My love has always been mythology. When I come across a book that utilizes creatures out of the depths of mythology, that really pulls me in. When I find one that changes known deities and creatures to suit some outlandish aspect of their story because they are too lazy to correct the story line.... Well, I think my words already express my sentiments.
It isn't easy to create a believable world based in fact or history or known concepts. I know my limitations on that which is why I only have one military science-fiction short story in publication. It was difficult to work beyond the character and make sure the science and technology was on point when I just wasn't sure about some of it. I'm not a scientist and I haven't worked in communications in many years, so my knowledge is not first hand.
History and mythology, though. Yep, those are aspects I'm more than happy to dive into.
My current novels with their focus on characters existing during the Golden Age of Piracy has kept me busy doing research about geography, known pirate ports, terminology, historical figures, and aspects of magic. I know my novel is fantasy, but it doesn't mean that I want everything in it to be 100% made up. I feel, for me at least, that a good story has realism. I also have a tendency to create a broad world which means I either create every societal structure from scratch and hope that I don't mess up some aspect of government, the economy, or logical evolutionary progression. Despite the side work, using history to build background is sometimes easier if also easy to make mistakes with.
What it comes down to is what works with the story you're trying to build. Since my premise is pirates in a certain world setting type, it is logical to use historical basis to help me. It also means that I can take past events and utilize them in some new, nefarious way for my characters -- what's more fun than that?
I like the research aspect and hopefully you will, too.