Definitive treatment covers split semi-simple Lie algebras, universal enveloping algebras, classification of irreducible modules, automorphisms, simple Lie algebras over an arbitrary field, and more. Classic handbook for researchers and students; useable in graduate courses or for self-study.
Make no mistakes, this book is a pain to read. Nevertheless, it deserves its five stars simply for the wealth of information it contains. There are plenty of results you will not find in any other book on Lie algebras, and many familiar results in much greater generality. And you will need them once you want to do some serious research on Lie algebras.
Unfortunately I have found some topics the author was trying to discuss not entirely clear and concise, some definitions I personally found vague. Mr. Jacobson should be more clear when discussing certain topics in the text. An example is Chapter 1 Section 5 on Representations and Modules; I found some ways where he was trying to explain not specific enough as eg xa=xA in defining a right module of the representation space. However, the book was exactly concise and clear in other topics; but this particular section I personally found frustrating