The Widow's Walk won't turn out the way you expect, but, then, what you expect will change at least three or four times before the end of the book. The writing is tight and the characters are vivid; there is a somewhat large cast of residents in the book's small-town setting, but there are never any moments of "who was that guy again?" You remember.
The book's pacing gets steadily faster. I try to read at least a chapter whenever I sit down to read, so I definitely noticed -- at the beginning, I stopped every chapter and picked up again a little later. By the middle, I had to read two chapters at a time to walk away comfortably, and by the final chapters I was breezing through as fast as I could.
The atmosphere is excellent. Christine does 'spooky' very well and doesn't rely on any cheap thrills or dangling a monster in front of the reader to make things scary. Erin is perfectly capable of scaring herself out of her wits without much help, and she will happily take you with her for the ride.
I will say the book is not a typical horror or ghost story; it's built up more around superstition and the power of small-town lore, and Christine uses both to good effect. I could be wrong, though; there's a thing or two by the end that just can't quite be explained...