I pretty much liked this book, but had two basic problems with it.
1. Way too much foreshadowing. From page one, you know something is up, but don't know what it is. Every single page re-inforces that foreshadowing, and it goes on through the whole book. You don't find out what the big secret is until there are only twenty pages to go. By that time, I was tired of the whole deal, and had really high expectations about what this big deal secret could be. Of course it couldn't live up to that, so the whole thing was dissapointing.
2. This book touches on all sorts of biotechnology ethics issues, but comes to its conclusions too fast. So Eli and Kayla are chimeras. And immediately they freak out and are mad (Kayla I can understand a little more, with the HD diagnosis and all that). Of course I don't think it's ethical to make experimental people, I don't even think it's ethical to make experimental rabbits! But there are a lot of good questions here, and the answers are much more complicated than the book allows them to be.
For example, there is that one part in the book, where Eli's professor is at the conference, and the man with Downs Syndrome gets up and asks why the scientists want to kill them. Suddenly, everyone is assuming an egg and some sperm is a human being, which is such a huge controversial issue. And with that assumption, all the ethical controversies are too neatly wrapped up. I guess what I'm saying is that I definately don't have the answers, but I like to think about it and weigh the different sides against each other, even if I never come up with an answer for myself. This book seems not really to think about it, but to leap to the ending. It could have left it a bit more open and messy in the end, I think.