Solid, if you like the series.
SPOILER: Dresden's first task as the Winter Knight: kill Maeve, the Winter Lady, an insane nature goddess and the daughter of his boss the Winter Queen. In the meantime, some old enemies try to kill him, some new enemies try to kill him, and some entities that don't care one way or the other about Dresden try to kill him. Just for being in the wrong place at the wrong time.

After the series high of Changes and the series low of Ghost Story, Cold Days represents a return to normal for Butcher. Dresden has leveled up again, and so have his many, many boss fights. (This is one aspect of the Dresden Files that I respect--most urban fantasy series I've read return more or less to baseline at the end of each book, but this one has Harry growing fairly substantially, losing allies and gaining new ones, dramatically growing his resources and responsibilities. It reminds me weirdly of Jack Ryan's ascension in the Tom Clancy novels.)

This installment is still funny, still packed with plenty of nerdly references (Princess Bride, Star Wars, Firefly, and a number of more subtle ones). Nobody makes 500 pages read faster than Jim Butcher.

But I do get tired of Butcher's habit of having Dresden get beat down, several times per book, only to be saved from certain death by the timely arrival of an unexpected ally. Dresden keeps coming off as weak and incapable. I know that if he's too strong to ever really be endangered, the tension leaks out of the story, but it's coming off unevenly. There's got to be a better way to handle it.