Would Kevin have been different with a different mother? That is the crux of the tragedy, to me, and it makes the book as great as it is, because there is no right answer here.
Personally, I found a great deal of common ground with Eva. She wasn't sure if she wanted a kid to begin with, and her feelings about her son seemed instinctual- that he was bad. There were times when she really, truly tried to connect with him and he spat it back in her face. The really sad part was that Kevin respected her for her distance, and seemed to loathe his own father who worked so hard to build a relationship with him.
Eva's character only bothers me when she refuses to pick up her life after Thursday. I don't know how much that little girl's family ruined her financially- I take it it was an OJ-type situation, where she wouldn't be able to make any money without it all going to the family? Huh, even though I thought she won the civil suit... Anyway, the point is, Eva has to move on from this point. I don't mean move on from Kevin- I think their budding relationship is, rightfully, a very important thing in her new life- but the loss and tragedy and depression. She has to straighten her back and show the world that this hasn't beaten her down.
I honestly should've seen the first twist coming, but this is one book I didn't spoil too much for myself. Even though I thumbed through a page that mentioned Celia and crossbow bolts, I didn't let myself think about what could be happening. But it did occur to me at one point that Franklin wouldn't have taken Celia away from Eva. It still hit me pretty hard, though, the way Kevin so carelessly offed his sister and father. Even I didn't see that much evil in him.
The second twist, though, for me at least, was that Eva really does love her son. I think that's what made it so much less depressing, that through all of this, the two of them can finally find common ground on which to build a relationship.
But that wondering if things could've been different... that almost kept me awake after I read it. How much of Kevin was a product of his environment, and how much innate? This book really raised some interesting questions about nature and nature and I'm really freakin' glad I read it.