I believe the most intricate plot won't matter much to readers if they don't care about the characters, especially in a series. So I try to focus hard on making each character, whether villain or hero, have an interesting flaw that readers can relate to.
“Let no one weep for me, or celebrate my funeral with mourning; for I still live, as I pass to and fro through the mouths of men.”
“It's true that I tend to daydream. I'm the same person in business as I am in music: I can be distracted and absentminded. It's my style.”