The book of Spinoza, the Ethics, was a companion of mine for all my years in high school. But eventually I started seeing some problems in his logic. There are good reasons I switched to Leibniz and Kant.
But as Jewish books go as far as ethics is concerned, the Ethics of Spinoza is powerful. 

The Ethics ("Musar") books of the Middle Ages e.g., The Duties of the Heart, are better than the Ethics. They avoid some of the problems you find in Spinoza. They are a little more modest about what we can know.




I forgot it, but I did have some way of defending Spinoza. I think it was something like this: What is an accident? Some characteristic of a substance. The difference between them is the substance is permanent and the accident can go away. A leaf can be green in spring and red in fall. But substances also change. In fact there is little that is permanent. What is it that these substances are accidents of?
It is this permanent substance that survives  all changes that Spinoza calls substance.
 This argument is what I used to try to defend Spinoza. Not that I am particularly happy with them but that at least we can understand what Spinoza was trying to get at.

Now if you want to give a critique on Spinoza, it would go like this. Even with this justification, that is still not a axiom. Typically an axiom in Geometry or Physics starts  with something self evident and almost trivial. For example if a=b, then b=a. You don't start with something highly counter intuitive and then try to make it into an axiom like "Nothing can affect a substance." [Even though philosophers do this all the time since Hume, it still just talking cleverly and making something dumb sound smart. ] For reasons like this. and several others(that Leibniz pointed out) I decided that Plato, Aristotle, Maimonides, and Kant were closer to the truth.

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Spinoza puts a condition of substance which almost forces his conclusion of Pantheism. 

 People claim for the Rambam the title of the greatest Jewish philosopher. Maybe he was, but the Guide for the Perplexed is the most perplexing book I have ever read.
They used to print it with the commentary of Joseph Albo. If you can get through it congratulations! I found it frustrating. And the medieval alchemy really bothered me.
But if you want to get to what Maimonides was saying without having to go through hell and back to find out, then the best book I ever saw is David Hartman's. And the Rav Kook Institute also had a very good edition of the Guide with a short but very good commentary.  Also Rav Kapach from Yemen had an edition based on the original manuscripts of the Guide with his own very deep commentary. If you have time I would recommend learning these and also Plato and Aristotle in order to have an idea of the issues that the Rambam was addressing in the Guide.