Somewhere in the 3 1/2 - 4 range.
Disclaimer: I received a promotional copy through the First Reads program.
Note: It's 258 pages, not 268.
It's a well-paced, entertaining read. The chapters alternate between Left Coast (mostly Porter and the film crew in Santa Johanna) and Right Coast (mostly Sam and his inner circle in the Buffalo area), and this works. Senna does a good job of keeping things moving, not wasting space with rambles. There are enough plot twists to keep the reader engaged. New characters are introduced as the novel progresses, adding layers of complexity to the story, but there's a sense of logic to these additions.
On the flip side, the characters are lacking likeability. Certain elements of the plot don't seem totally plausible, so nit pickers will enjoy this less than people who can just go with the flow. I'm not so sure about the ending.