I read book this immediately after reading "Rich Dad, Poor Dad", the first in the series of Rich Dad books. Rich Dad's Guide To Investing continues the central concept of comparing his biological father ("Poor Dad") to his best friend's father ("Rich Dad") as a means of contrasting how the Rich and the Poor differ in their attitudes towards money. In the first two-thirds of the book, Kiyosaki repeatedly hammers home the point that one of the first steps to achieving great wealth is a change in one's attitude towards money and indeed, how to make money. He emphasises the need to build a business and become an investor in business rather than work as an employee. It's similar stuff to the (perhaps eye-opening) first book but it doesn't hurt to read it again, especially if your attitude towards money is more aligned with that of Poor Dad. And for me it's this that makes it worth reading.
On the negative side, and admittedly this may be a symptom of reading two of his books back-to-back, things get very repetitive; the book really needn't be 500 pages long. At the end he descends from the high-level lessons and actually goes into some of the specifics of how to take a company public! It smacks of gloating as nobody considering taking a company public would be reading this book for advice, especially since at the time of writing, Kiyosaki had never (and maybe still hasn't) taken a company public before. I also grew to dislike his writing style, perhaps because some of the concepts are over-explained and therefore at times you feel like he's talking to you as though you were a child.
Two other things that irritated me: Firstly, the ceaseless promotion of his own board game that he developed with the 'noble' mission of elevating everyone's financial literacy (or words to that effect. The game is nobly priced at almost $200!). And secondly, the pointless interjections from business partner Sharon L. Lechter which serve only to interrupt the flow of the book.
On the whole it's worth a read but don't be afraid to but it down when it starts to get tough going towards the end - you're better off picking up your next book.