The concept of natural selection has certainly 'evolved' since Darwin penned this work (pun intended!).
While scientist have greatly expanded from the seed of origins that Darwin planted with this work, it was an interesting visit to return to this book. I found many of the social moreys a bit staid and perhaps slightly tainted with bigotry; like the abundant usage of 'civilized and savage societies'.
Also, one must remember that the simply idea of natural selection is no longer the preferred entirety of the modern evolution theories. So, much of the science of this work is very simplistic. For example, Charles Darwin could not have forseen all the complexity that is found in DNA and RNA.
A reader must be prepared to accept the verbiage of 1800's Victorian Era scientific jargon, with a bit of an overly simplistic view of evolution. However, if you want to read the book that started the Evolution Theory this is the place to start. It is the Origins of Evolutions (another pun, but I groan).