Best What's new book about just changes and new features in SQL Server 2012
You could always read the what's new sections in the BOL. As for a book, have you looked at Microsoft's free book? A hard copy is available too, if you prefer. The book is not a coursebook but more general an approach. As per introduction:


  Who Should Not Read This Book
  
  As mentioned earlier, the purpose of this book is to provide the
  reader with a high-level preview of the capabilities and features
  associated with SQL Server 2012. This book is not intended to be a
  step- by-step comprehensive guide.