I've only flipped through that one. I seem to recall it being generally pretty decent. Reb Zalman is really a mystic at heart, and he is very big on the power of the moment, and connecting your spirituality to the emotional strength of religious experiences. Which is good, and right, and a very important truth that much mainstream Jewish practice has neglected of late. But, at least in my view, it's also important to balance that extremely important development of spiritual potency with the obligations and duties Jews have under the halakhah (Jewish law). For example, with prayer, of course it is vital that prayer experiences be meaningful and powerful and spiritually affecting. But the nature of people as spiritual beings means that such an experience is not likely to occur each and every time we pray, if we are praying daily (or three times daily), as the tradition tells us we are obligated to do. And that might be okay. I like to think about it like baseball: Hall of Famers hit .300, maybe .400 tops. In other words, for every 10 at bats, they're striking out 6 to 7 times. But you get up to the plate, and you take your at bat, or you take your swings at practice, and you do so not with an expectation to hit every pitch, but with the knowledge that every swing you take keeps you fit, keeps you sharp, makes you a better player overall, and that even those times you whiff big time and miss the pitch by a mile, you're still at least in the game, and it all goes to bettering your skill as a player. You see what I mean? And I think that's why Reb Zalman tends to lost sight a little of why it's important to keep at observance of the commandments even when you might not feel 100% motivated or in the zone for a peak spiritual experience. But you know, he's still totally worth reading, and his message about spiritual richness is a good one, and much needed.
Just off the top of my head, I recommend, of Reb Zalman's books, Wrapped in a Holy Flame: Teachings and Tales of the Hasidic Masters, and A Heart Afire: Stories and Teachings of the Early Hasidic Masters (co-authored with Netanel Miles-Yepez), and Tanya, the Masterpiece of Hasidic Wisdom: Selections Annotated and Explained. I thought these were all really excellent and both useful and informative sources on the thought of the Hasidic Masters. And they were very important, I think, because they were also seeking to reinvigorate the practice of Judaism with ecstaticism, which is more or less what the best of Jewish Renewal is trying to do-- the Hasidic Masters just did it with much greater erudition, subtlety, and traditionalism.