Geron's book is more of a tutorial/cookbook coalesced with important insights into the practice of machine learning. So, I recommend reading Introduction to Statistical Learning (and Elements of Statistical Learning for theoretical background) before jumping into Geron's book. As engineers, I agree we need to have some theoretical background but at the same time, we are applying this knowledge to real world problems. Geron's book is invaluable and I hope publishes more, it is a gem.