Basic Category Theory is cute, but I think the exercises are sometimes phrased strangely.  In some ways, the book makes more sense if you've already seen these ideas once & are trying to get a more CS perspective of the math.  I'll probably be alone in this, but I think Mac Lane is a fantastic book for learning category theory.  It's hard, but if you trudge along and do the exercises you learn quite a bit.  It's fun!