I just reviewed what I firmly believe will be the book that will replace MacLane as The Gold Standard for introductions to category theory for graduate students: Category Theory in Context by Emily Riehl. It's developed over the last several years from courses in category theory that Riehl has taught at Harvard and John Hopkins University to strong undergraduates and first year graduate students. She posted her evolving notes at her website each time and the first time I saw a rough draft, I knew she was writing something special. The finished text did not disappoint. It's comprehensive, incredibly clear and amazingly rich in examples, including many you've probably never considered. It's a remarkable book and I think it's going to replace MacLane very quickly once it's known to most experts. Best of all,it's much cheaper then MacLane!
If you're interested in category theory, this is the book you want to learn from. I wish it was the one I'd learned from.
My full review can be found here.