It was screwing with the audience for all the right reasons.
Yeah I thought Ellen Page was annoying, but I kind of think the audience was supposed to find her annoying, and side with Patrick Wilson's character. Then when the truth comes out it's supposed to make you reconsider who you're supposed to feel bad for.
It was one of those movies that aggravated me so much while I was watching it, but it had me thinking so long afterward that I had to admit that it succeeded, it was great for what it was trying to accomplish.