britbox
Multiple Major Winner
I'd say the books were followed pretty closely the first 4 seasons. I read up to where the show left off at the end of season 3 and from what I read the changes in season 4 were not material. From what I've heard from people who've read all the books is that season 5 was a huge departure in many ways..
I've got all the books but not just read them yet - started the first one and will eventually plough through them but based on what I've read so far, I prefer the TV adaptation and that's fairly rare for me. I think the show is that exceptional, I couldn't care less with how they correlate to the books... the tail has started wagging the dog.