The worry of the second book in a trilogy that starts off well is that the author will have blown all his or her good ideas in the first book.
Luckily, this is not the case with The Twelve. In fact, Cronin has become a better writer than he was when he created The Passage, the first book in this series.
The Passage was a great example of world building that got hampered by one of the most clunky reboots in popular literature. But, it did have great characters and a great premise so was fun to read.
The Twelve, on the other hand, avoids the reboot problem, fleshes out a more interesting story and lets the actions of the characters continue the world building - which makes for a much better read.
At the end of the day this is what a modern vampire story should be. It's scary in a way that Stephen King hasn't been in years and it doesn't romanticize the vampires.
Instead it gives a series of incredibly dark events involving characters we care about, even though we know they are doomed.
It has a bit of G.R.R. Martin Syndrome - in that it seems to give us more characters than we could possibly follow, but simplifies things by killing them off on a regular basis.
The result is a tight, terrifying interesting book where anyone can die at anytime all living in a world we really care about.
It's awesome and awful and beautiful and horrifying all at once - which is how it should be.