Categories for the Working Mathematician

Being one of the fathers of category theory, Mac Lane did much more to averse people from CT, than many category haters. Poorly structured text, esoteric stuff, many proofs left as exercises to the reader and uneven writing make this book bad choice for beginners. This book contrasts with ‘Algebra' written in collaboration with Birkhoff. If you want to start with Category Theory, you'd want to begin with Awodey or even better choice IMO - Tom Leinster. While being pretty complete and widely acknowledged handbook on CT, it's thorns and pure evil for beginners.