For an introduction it was ok to get some of the concepts and what is possible with/in Riak plus it contained some guidance on the typical pitfalls and covered both developer and operational topics. Maybe a little light on what was added in version 2.0, but as the title says it is a 'little' book. If you want more in-depth knowledge, then look elsewhere i.e. to the documentation by Basho.
Some books are written to be read. Some others deserve... well.. they rather need to be decoded! Unfortunately, this one is part of the second category. Obviously, the authors know their subject: they are part of Ruak's core developer's team. Despite of that, the key ideas missed to be introduced clearly. At the end we get that the ring is a key architectural element. Short doesn't means synthetic all the time. The format is indeed very short (less than 100 pages) but isn't a good introduction. Ma note de lecture en Français ici