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.
“I had the chance to visit all 56 counties in Montana in my pickup. You can put Washington, D.C., in one corner of our state and put Chicago in the other corner, and that's the size of my congressional district.”