3.5, rounding up for the unusual and well-done love triangle. I could have chosen to round down for some of the clumsy (in my opinion) SF (sorry, I couldn't make head or tail of what [spoiler] was doing with the birds, or how they got out), but the book was fast and pleasantly page-turner-y (I don't always find that pleasant), and so I'm generally happy with it. 
 It is kind of begging for a sequel, I have to admit.