"The flip" is when someone's perspective about the material world flips around, recognizing the metaphysical as just as real as physical reality. This book is about this process, delving into stories from scientists and other accomplished people to show how the material world is not all there is. It paints a picture of how materialistic reductionism is certainly not true, and consciousness is a fundamental part of reality.
To that extent, it was amusing, but aesthetically felt like wildly waving hands in the air. It offered story after story and many perspective against materialism, but didn't actually construct any cohesive, falsifiable (or testable, or critiquable) view. "Here's a super weird thing that happened that science can't explain..." over and over. The book wasn't about one specific spiritual path or belief system — in fact, it was fairly clear that established belief systems are hollow. Overall, I couldn't quite figure out what The Flip actually wanted of the reader, other than for the reader to muse aimlessly about consciousness.