I believe "First Fundamentals" is an important book. It contains a huge amount of material in form of bite-sized pieces, though those bits are like highly concentrated energy food and more nutritious than the more voluminous Go-educational meals that are often recommended to players who this book is intended for. It's a good format because the student can pick a principle and read the relevant paragraphs that follow the heading within just a few minutes, then study the examples and apply the newly learned ideas immediately. The principles are all to the point, there's little fluff here, though it's nevertheless "readable" and doesn't put you to sleep.
The advantage is that you don't need to (and really shouldn't) read the entire book in a couple sessions, and can instead learn about a principle and then go and play a bunch of games before tackling the next section. Robert always struck me more as a heavily theory-focused person (which had initially discouraged me from looking into his works as I'm more of a practical-minded person who quickly loses focus when reading dry explanations and complex, boring excursions), but First Fundamentals is definitely a very praxis-oriented, "hands on" book whose format resonates unexpectedly well with me.
I was surprised at the unusually large number of examples in the book (I'd estimate that there are at least 4-5 diagrams per page on average), and it's not chiefly the "this is how you do it" kind, but the majority of diagrams show how to not do something. This is interesting because many of the examples shown don't appear (to the target audience) necessarily as wrong (which is why we like to repeat our mistakes all the time!), so they stimulate a critical review of one's own feelings on positions and how we instinctively (but inefficiently) respond to them.
I've already found various positions where I stared at a "wrong" diagram and thought "But this is riiiiight!!!", and then dove into trying to understand why it in fact wasn't "riiiight". Those kinds of situations really help me to learn and alter my established pattern and errors. Noteworthy is that the examples often feel real: the stuff you experience in DDK and SDK games, which makes them tangible and easy to relate to, without seeming artificial, contrived or isolated from the context of every day matches.
I am unsure who the book is best suited for, especially after only spending a few hours with it. I believe it covers a fairly wide range of "ranks", partly because of the scope, partly because kyu players up to at least mid SDKs have such wildly varying knowledge bases. I'd say it's one of those books that grow with the reader and that yield new insights from every re-read, because what you can take from it depends on what you already know. I can't really judge suitability for people stronger than 6'ish kyu because I'm just not there, but there's been plenty of stuff that I felt was a little advanced, so closer-to-dan players can probably benefit as well. I feel that it makes an excellent "second" book, or maybe a third one, and I believe for a DDK it fits in perfectly after "Opening Theory Made Easy" (and is not a replacement for it, in my opinion). For SDKs, it's good at any point.
Unrelated to the content, Robert delivered the book (and the PDF, which came free with the physical copy and was e-mailed literally an hour after sending the payment) promptly. Even the "shipping cost free" variant within Germany was better and more securely packaged than what you normally get even if you do pay for extra packaging (when you order the extra secure option, it probably comes in a 10 times larger box and an armful of packaging materials!). He also signed it on request, which added a nice touch from a collecting point of view.
So, in summary, my first impression of First Fundamentals is surprisingly good and I would recommend it to people who like to really work with a book, not just skim it or read it through and then move on to the next. The content/price ratio is exceptional and you really do get something for the money. I'll also say that the book has made me more curious about Robert's other works and his qualities as a teacher. It's very different from the impression that some posts occasionally give (those stickler-style arguments about rules ...
In short, First Fundamentals is good stuff.