I would say that Robert repeats himself a fair bit, which, is to be expected so as to make the books all self-sufficient, but, it can be a little annoying to read an entire book with 12% new content.
To avoid these pitfalls (as I have read all of his books) I thought a quick reference guide as to which books to read (and in which order) and which to avoid might be helpful.
These books are also graded with a "buy for future and ongoing reference" or "read once" as, unless you already have a hefty education Jar (see Millionaire Mind), you might not necessarily have the funding for each of his books.
Rich Dad, Poor Dad (The original)
This book has a special place in my heart, as, it was the very first book I read in regards to passive income, time leveraging, and other money making concepts. As a result, it is difficult for me to be unbiased, but, I will say that it is an excellent beginners reference, and, fairly useless to a non-beginner. Good for a single read, however, I have purchased many copies over the years to give to people interested in learning of passive income, so, if you are starting a multi-level marketing team, you might want to buy a few to have around the house to give to your downline.
Rich Dad's Increase Your Financial IQ
A dad more wordy than his other books, but a fair bit of useful information. Tends to lean towards American-only information, but, even as a Canadian, I found this one eye opening.
Why We Want You To Be Rich
Borderline useless. Could have been summarized in the jacket of another book, honestly. But then again, I rarely need "convincing" from my authors. If you are the type of reader who demands countless pages of credibility building, then this one might be good for you.
Rich Dad's Cashflow Quadrant
His best work, in my opinion. Definitely a great read, full of information that you will repeatedly reference. Buy this one.
Rich Dad's Guide to Becoming Rich Without Cutting up your credit cards
Useless and all repeat information. Kind of like the first book and a few others in a different order.