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.
“We do not have a money problem in America. We have a values and priorities problem.”
“I was a fighter pilot, flying Hurricanes all round the Mediterranean. I flew in the Western Desert of Libya, in Greece, in Syria, in Iraq and in Egypt.”