I actually, before coming across this book, thought about someone with this 'superpower' to take over a person's body whenever she wanted to, but she didn't really want the power, but sometimes she can't control it. So.. lol.
I liked the fluidity of A, although... I can't help but assign the author's gender to A, even though A is supposed to be genderless. I liked that the author tried to include all sorts of people in A's life (but I was disappointed in his treatment of the overweight boy; and Rhiannon's reaction, although realistic, was not really addressed but just glossed over).
I feel sad for A that he doesn't get to experience tomorrow, but I thought it was nice of him to leave Rhiannon with Alexander, even though it feels like a cop out. I think Rhiannon as a character could be more developed; it just feels like she is defined first by her love for Justin, and then by her love for A... yes, she has friends and a life, but I never knew her goals in life, her history - her conversations with A seems to be a platform for the author to introduce more days of A's life to the reader instead of delving deeper in Rhiannon's story. So I feel that's a missed opportunity there. But then I realize this story is about A, not her. I do like A's musings though, but I don't get how he could fall for Rhiannon so quickly and so deeply. But that's just me.