Better than the vast majority of his new books. With all the attention focused on a traumatized little girl and little (if any ) focused on Koontz whining about how much he hates modern society or Hollywood, makes this book a winner.
Characters: Here they are alright, but still somewhat cookie-cutter. I read the book only a month or two ago and I've already forgotten the psychiatrist's name (she was one of the main characters, so that's really not good). I just checked and her name is Laura (same as the Lightning protagonist, which I didn't like). She is shy and withdrawn due to a bad childhood. Very common for a Koontz character.
Lt. Dan Haldane is far more interesting. He's serious with people that he likes, such as the psychiatrist, and generally jokes with the people that he does not, like his rival Cpt. Ross Mondale. Of course, being a Koontz character, he's tough and capable. No complaints here on that subject. He preaches about the state of the world a little bit, but this is 1980s Koontz and he doesn't get on his soapbox for too long.
Plot: The plot centers around the psychiatrist's daughter, Melanie. Melanie is deeply traumatized and catatonic after seven years in a deprivation chamber, and Laura must get her out of that catatonia, and find out what is the "Door to December" that her daughter keeps whispering about. However, Laura also realizes she's being hunted by the authors of Melanie's misery along with some unseen entity that is dispatching people with superhuman force. It is up to Lt. Dan Haldane to solve the case. It's a great plot, in my opinion, with mystery, a good smattering of action, and hints of sci-fi, just like Lightning.
Climax: Actually pretty bad, which was a surprise but not a big surprise with Koontz. The gap between the revelation and the final resolution is far too small, probably not more than five or six pages. And the revelation isn't good either. You're going to see it coming from a mile away in slow motion.
Prose: Somewhat mechanical. This really comes across in the way characters, like Laura, overthink to themselves. Like with Lightning, there are cases where Koontz could've used a 5 cent word in place of a 20 cent word. Still...bizarre, obscure words that nobody knows are extremely rare in here. As are long-winded metaphors and descriptions. You won't get a sense that he was writing with a thesaurus next to him (something that New Koontz more or less admitted in an interview), and trying really hard to impress people whom just want a good thriller with no bullshit.
The metaphors and similes here seem to be in a balanced amount.
"Hard spikes of cold rain nailed the night to the city."
This is the second paragraph. It does a good job illustrating the power of the rain and night sky without being verbose. Likewise the imagery used in Door to December all seems to be just enough explanation without over doing it, as he does in recent efforts.
I don't know where exactly to put this but it's worth noting. Early on, Laura is thinking about her parents that she was estranged from. This was because they were "religious zealots." Koontz, in this day and age, will never put those two words together like that ever again, at least not in the context of Christianity. In New Koontzland, there are no Christian extremists but bad atheists, bad professors, and bad scientists.
It's perfectly readable, and I honestly wish Koontz would come back to this old style of writing.
Highly recommended.