I've just finished it and I loved it. I was gutted when I realised I'd finished it though, I was hoping there'd be another chapter. I really wanted to know what happened to Circuit.
The only bit I didn't like was Fanning getting his happy ending with Liz (in the afterlife I presume). I don't think he deserved it. I know he was heartbroken when she died but that didn't excuse everything he did.
I think there's scope for more books. I'd love to hear more about what happened to Caleb, Pim etc after they got to the island. How did they rebuild a society that sounded very much like our own? On the subject of which, after a thousand years wouldn't you expect that society to have evolved/changed somewhat? Maybe that bit wasn't very well thought through.
The other thing I'd have really liked is more of a scientific explanation of what the virus was, where it came from, how it worked, why Amy was so different etc. I like the nerdy science stuff in theses types of books.
I also cried when Amy carved the names in the stone and it's not often a book makes me cry.