Remember Yesterday, by Pintip Dunn
The premise of this (probable) trilogy is so unique (time travel involving twins born at different times), and I really enjoyed not only the science but the philosophy behind it all. The characters were complex and intriguing, as well.
Here's the list from the first half of the year: http://robinellen.livejournal.com/576950.html
There were more five-star re-reads than there were first-time...but that's not surprising, considering that I re-read them because they're so good, in the first place. :)
Soon, I'll post my first reads of the new year (I'm already behind in posting, so there are a few of them). Read on!