This was one of the most well-rounded personality books I've read. I've seen a lot - Myers-Briggs, ones based on color or animal, introvert-ambivert-extrovert spectrum, and so on. Dondi Dahlin writes about the "world's oldest personality type system" in a breakdown of five elements: water, wood, fire, earth, or metal. The reason this is so well-rounded is that it doesn't try to peg the reader into a single category, but rather into primary and secondary elements.
If you're intrigued, you can take the personality quiz here! I took the inventories in the book for myself and my husband and kids, and it honestly did give some insight into how we're the same and different, explaining why certain things lead to conflict but others lead to increased compatibility. The book not only explains all of the elements, but it also helps readers learn how to parent children with the same or different elements, and how to grow as a person using main elements as strengths.