I don't care if the original idea / concept is original or not. Fact is: Alone, is enough to make you read the book. And it is enough to make you keep reading it. Even if the book itself ends up not meeting initial expectations. 
 This could be a better book, a book that could rely on more depth beyond the initial concept. But I liked it. 
 I thought that the narrator was confusing. Would be so much more interesting if we could have Lucy's point of view as the events unfold. What was she feeling? What was she thinking? Instead, we are given a full report of Daniel's lives. 
 The soul connection is only nearly explained near the end. In the beginning, Lucy is simply a new and different person, not connected to her other lives. There doesn't seem to be a valid reason for the fact that she is "his soul mate"! He is simply too obsessed with her memory rather than the person she is during her current life. 
 The End: I do like open endings. This one could be much better though. 
 Please make a movie out of this. If done right, it can be great.