The other book I got for Christmas (SJ Watson was the first) was Sister by Rosamund Lupton which I did like and it took a longer time to work out the "baddie" which is always a bonus. I did enjoy it, unusual perspective as the main character is trying to understand what has happened to her sister. 
I liked the characters much more that the SJ Watson book (I really didn't care about any of the characters in that book which is a big negative for me - they were neither interesting nor likeable in any sense) The characters in Lupton's book were both intriguing - sisters but very different.