My first reaction, of course, was EVERYTHING IS WRONG WHY DID THEY CHANGE ALL THIS AAAARGH. The basic premise of the series remains: Harry Dresden, Chicago's only professional wizard, consults with the police department to solve cases involving the supernatural. But most of the details have been altered. Instead of wielding a rune-covered staff, Dresden wields a...hockey stick. Instead of being a crass, wisecracking talking skull, Bob is an occasionally crass, mostly proper British ghost who lives in a skull. And so on and so forth. Backstories, names, personalities: changed! They do make two notable changes to increase the racial diversity of the series, though: Lieutenant Murphy becomes Latina and Morgan becomes black. (Sadly, one of the few characters in the book series who is not white becomes white in the TV series, but since she's only in one episode, it kind of evens out? Over centuries of white supremacy? I don't know.)
But to judge the series as an adaptation would do it an injustice. You don't have to have read the books to enjoy the series (and, in fact, you're more likely to enjoy it if you haven't). How does the show work as an urban fantasy series?
Fairly well! The show does have its hands tied by making Murphy ignorant of magic, which makes her trust in Dresden slightly mystifying, but otherwise, it's as fun as expected to watch Dresden and Murphy solve cases together, with the help of a centuries-old ghost who has a treasure trove of knowledge. I appreciated that the show made up lots of cool magical detectiving ideas that are not in the books. Dresden does face some of the same foes from the books: vampires, werewolves, bodysnatchers, etc. But most of the stories are wholly original, and they acquit themselves well, frequently doing the Supernatural thing where you spend half the episode thinking the villain is one thing when in fact you've been looking at it all wrong.
(The special effects are crap, though.)
Even though the early episodes are a bit rough, the show's main strength is its excellent cast. Paul Blackthorne nails Harry Dresden, world-weary and sarcastic, delivering dry, noir-ish voiceovers. Terrence Mann, though not the Bob of the book, is a delight every time he's onscreen. Valerie Cruz, though not the Murphy of the book, balances warmth and tough-nosed cop. Conrad Coates leaves a lasting impression as Morgan, the Warden (wizard cop) who's always cleaning up after Harry and also blames him for everything because black magic.
For about half the series, we get worldbuilding and character development, and about halfway through, continuity begins to kick in, and the series upgrades from mediocre to good. And then its last few episodes, it upgrades to really good, as it finds its voice, how best to tell stories with the characters it has in the world it's created. You guys, obviously a ghost can't die and the show still made me fear for a ghost's life. It does such a great job grounding everything that the magical elements never seem absurd or out of place, and even though it keeps things light at times, it understands that it needs real emotional stakes, and it goes for them.
The Dresden Files only lasted 12 episodes, and although it never comes close to attaining the brilliance of the book series—which has a much larger scope—it had the potential to become something very special. Thankfully, it does not end on a painful cliffhanger. I'm glad Harry Dresden got to be on television, but it's too bad he didn't set SciFi on fire. Er, in a good way.