Somewhere I saw Spinoza described as cryptic. If by 'cryptic' is meant 'hard', this is agreeable. But Spinoza in no way intends a linguistically obscure work: all the terms come from long-established scholastic traditions, and he defines what is meant by them everywhere. More challenging is to understand how these parts interact: and this is where the consistency appears. The 'Ethics' is a metaphysics, a theology, a nature-philosophy, an epistemology, and many other things as well, and every piece fits seamlessly with the whole. It is satisfying to see come together, and worth the length and density of it, which is nothing compared to post-Kantian philosophy.

Descartes' Meditations is the work to read before reading this, it was the ascension of Cartesian philosophy that inspired Spinoza's own, and Spinoza answers the problems his gives rise to. (One of the Germans describes Spinozism as "exaggerated Cartesianism.") It's very interesting how Malebranche, Spinoza, and Leibniz all need (in some way or other) the direct role of God to establish contact as it were between mind and body, where Descartes doesn't. In all, a classic of philosophy, and well worth reading.