This book also has the [backing of Peter Smith][1], who is basically the king of logic-related reading materials (logicmatters.net). I was part of a student reading group studying BCT last year with him, and I found it extremely helpful in the context of people studying for the MMath. One of the most important parts of basic category theory is seeing how adjunctions, limits and universal properties play with each other; this book is about exactly that, and goes into it in a depth I haven't seen very well elsewhere.

[1]: http://www.logicmatters.net/2017/01/02/tom-leinsters-basic-c...