Hello. I am about to start learning category theory. I keep hearing mixed opinions on the book Categories for the Working Mathematician, by Sanders MacLane (I am aware he is one of the founders of the theory). Some say it's a "must read", and others have called it "outdated." What would seem outdated about this book? What would be the pros and cons of using it? Is there a book or a collection of books that you feel cover the same (or more) material but better? IF any of my background is needed, I have a fair amount of mathematical maturity. I can read Rudin, Lang (Grad algebra), and other such terse books and fill in or construct my own such proof fairly well when things are missing. I might just be shaky in terms of knowledge, such as definitions etc. For example, I haven't learned algebraic topology yet.