This is the pinacle of the tradition of medieval scholasticism, and one of the greatest works of essentialism. Written in reaction to the birth of modernism through Descartes and Leibniz, Spinoza creates a compelling work organized as a geometric proof for the correctness of a virtuous life. Along the way, he "discovers" concise definitions and formulations for human emotions, virtues, vices, desires and ultimately freedom and bondage. These descriptions are extremely useful, even if the ultimate conclusions of the exercise (including rejection of all emotion other than a somewhat cold intellectual pleasure) are unpalatable.
These conclusions are naturally predicated by the axioms constructed for the purpose, and they expose the majority view of Spinoza's day as an uncomfortably incomplete formulation that is rooted in essentialism but fails to follow through to the logical ends, resulting in an inconsistent and erratic view of human morality and virtue. A similar worldview is prevalent today, but in the modern context the text seems to do more to highlight the limits of essentialism in general and the scholastic tradition in particular, reinforcing the importance of existentialist considerations rather than convincingly defending rational essentialism. The work therefore takes on the peculiar quality of an argument that fails in its initial aim but acts as a unique and essential (sorry) part of larger discussion. I can understand why Kant asserted that all modern philosophers must first be followers of Spinoza along with Plato.