The book "Essential Quantum Mechanics" is an excellent complement to standard textbooks on quantum mechanics. It shows a very good insight into the quantum states, the eigenfunctions and eigenvalues, the operators, and the observables. It has an excellent treatment of the subject of bras and kets, and matrix representation of vectors and operators. The book has helped me in better understanding these mathematical computations. The book is not a stand-alone text on quantum mechanics for it does not have all the historical background and experiments that led to Q.M but it is an excellent reference that can help clarify concepts and computations, and for this it deserves a very high rating.