Conversationally Speaking is surprisingly subtle and deep despite or perhaps because of its simple, straightforward language, methods and anecdotes.
Many a time, at the start of a chapter, I'd think, "where's Garner going with this", or "that seems a little obvious" only to be completely surprised and profoundly taken aback by his shrewd observations and wisdom, a few pages later.
This book bears multiple readings because it has much to say in despite being concise. I especially like the chapters on Self-Disclosure, Self-Defeating Rules, and IDF (Idealization, Frustration, Demoralization) disease, which were real eye-openers.
If I have any criticism of this book, it would be to say that, like many a self-help book (like The Seven Habits, and First Things First), it features many proactive strategies, in this case for overcoming shyness and improving all relationships, but it doesn't deal with the limits of those strategies, i.e. it doesn't overtly state that sometimes the best thing to do is cut your losses and ditch a relationship that's not working. Instead there is an implication to not give up on anyone, and to shrug off others' bad behaviour, rather than trusting your intuition and calling it what it is.
Keeping that in mind, the book is still worth every penny.