This book stands outside of the normal Dresden Files series. It's a novella written from the point of view of Thomas Wraith, Harry's brother. Butcher is the author, Mignola is the illustrator. It's not a graphic novel, it's a novella with a few illustrations.
I thought this was a pretty good book, however, it was also a lot more heavy handed than the rest of the Dresden books. Thomas does an awful lot of "I'm a monster" agonizing and while I agree it's a tough life... he's really very whiny, moreso than when things are from Harry's POV. Still, it was really interesting to see things from Thomas' point of view. His affection and admiration for his brother come through quite clearly and that was a real pleasure to read about.
It was also fun to see Thomas interacting a bit with Bob.
Harry doesn't usually portray himself as one of the most powerful living wizards, good, but not on that level, so Thomas' view of him raises some interesting questions.
I'm a little wary of this whole "Oblivion War" thing. It's certainly an interesting concept, and I like the idea that Thomas has things he wants to protect Harry from, and that there are some really big bad wars even Harry doesn't know about. Having said that, was the spam header in the e-mail really necessary? Could they not just pretend they're talking about Bethesda's Morrowind game of the same name? I'm curious to see if this will turn up in the main series (I suspect it might).