The Dresden Files is a series of urban fantasy/ detective novels set mostly in Chicago. The novels are written as a first person narrative from the perspective of private investigator and wizard Harry Dresden. There are currently 15 novels in the series and a handful of short stories. Each novel is a complete novel, however, the series is best read in order since various characters make re-appearances and past actions have future consequences.
The Dresden Files series starts off as a set of "simple" investigations into supernatural shenanigans, but evolves into something more intense and complicated. As the series progresses, Dresden takes on an increasingly important role in the supernatural world at large as he works to protect the general public, making it difficult for him to get by as a working wizard and private investigator. He finds himself dealing with an increasing variety of creatures (including other wizards), while facing the realization that his more difficult cases may all be tied together behind the scenes and that his role might be even greater than he is willing to admit.
Everything from vampires, demons, spirits, old-world faeries, werewolves, Sasquatch, other cultural monsters/ gods, ghouls, resurrected dinosaurs, pizza addicted little fairies and Tibetan Temple dogs (got to love Mouse) make an appearance. Jim Butcher manages to flesh out his world by providing each set of supernatural creatures with their own, interacting set of political and social rules and organisations.
The first 3 or 4 books in the series were enjoyable fantasy. The following books just keep getting better and more intense. Not everything is sunshine and roses for Wizard Dresden, and events don't always end "happily-ever-after". There is growth and development (in one way or another) for even the minor characters. Jim Butcher takes some old concepts and turns them inside out to produce this set of original, delightful and entertaining novels.
NOTE: There is a television series with the same title that is very loosely (i.e. almost no resemblance) based on the first few books. The books are a million times better than that series.