I enjoy reading long series of books, so that I can really get to know the main characters. My specific chosen genre is historical detective fiction and must say am spoiled for choice with so many really great writers covering this.
I am currently immersed (audible books for me as cannot manage to read late at night) in Sam Burnell's Richard Fitzwarren ten books. These are not detective ones, but good, exciting stuff set around mid Tudor times.
Of course, nothing at all can beat (or really be as good as) CJ Sansom's wonderful books, I have listened to whole series at least three times and each time they bring something new to me,
Susanna Gregory has a long and enjoyable series in my chosen genre set in meadieval Cambridge, Andrew Taylor's great stories in 17 century London. Then there is Ann Swinfen' series and, of course, the Master of it all, Bernard Cornwell. Plus many, many more.
The amount of great research that goes into books by these authors always amazes me. I love social history - what people ate, wore, etc. is so much more important than which monarch sat on the throne - and these books cover this extremely well.