Most of the original text and sketches have of course been lost either by time or by Leonardo's own design (he deliberately corrupted his own texts to keep his competitors from stealing his works
). It is a true shame that this knowledge is lost.
Any free kindle edition is easily worth 4 stars. It is a rare treat to see Leonardo's mind at work. He was one of the most gifted intellects ever created and just watching how he 'pieced' the workings of life and the known universe together is worth the time and study.