This is the case with Jim Butcher and his Dresden Files series. Storm Front is the first in his series about Harry Dresden, Chicago wizard. Harry is a wizard for hire, and from the first novel, you get sucked into his dual worlds of modern day Chicago and the world of wizards, werewolves, vampires, and every supernatural creature you can think of. They intersect through Harry, and each new novel finds him growing stronger in his wizard skills, and getting into deeper trouble with the White Council, the Red Court of Vampires, and the Faerie world.
You need to start at the beginning; each new novel builds upon the previous exploits of Harry. His faithful side kick is Karin Murphy; a Chicago detective in charge of investigating "unusual" crimes in Chicago. Their relationship is complicated and one of the best developments of the series.
I just finished Turn Coat, which is the eleventh in the series. Butcher doesn't seem to have lost any steam; Harry still has plenty of adventures left to tell. I've enjoyed each story and the ties that Harry has forged over the years with not only Murphy, but his friends Michael, Will and Georgia, and so many more characters I can't mention without giving too much away!
Changes has just been released, and I haven't had a chance to read it just yet. An old flame from the past comes back with disturbing news for Harry and sets him off on another dangerous quest. Will he survive again to fight the dark forces that are threatening to overtake both our world and the nevernever?
If you're looking for another great series, try this one. It's kept me intrigued for many years, and each story is captivating and a nail biter to the end. This series would be great for teens who have grown beyond Harry Potter and are looking for other wizard novels. They are funny, a bit dark, and will keep you on your toes putting all the pieces together to solve each novel's supernatural mystery.