This is my first review so I'm going to keep it short and I apologise if it's not that helpful. The biggest strength of this product lies in the depth and detail it goes into in describing its setting, based on the seminal 'Roadside Picnic' by the Strugatsky brothers. It describes a number of different anomalies and artifacts and gives ideas and help for creating your own as well as going into detail on the elements of life in and around the Zones in the setting. One of my complaints in this regard however is the fact that the PDF ultimately only goes into detail on specific Zones in the setting with the Zone in France and touches upon Zone Japan, otherwise skimming over the other areas with a few details. Nonetheless the PDF still provides a useful detailed overview of Zones generally and this somewhat vague nature in the way some of the zones are described might be preferred by some people. The presentation of the book is fine with some good art and I only noticed one typo.
My biggest worry with the PDF is that rules-wise it follows a diceless system created by the developer. I have not ran any games with this PDF yet and so I'm not sure how well the system used ('Flow') works and this may put off some people from running a game with this PDF. A dice conversion can be found on the publisher's website but again I do not know how good it is. The PDF also doesn't go into a lot of detail in exploring mechanically how enemies, the anomalies and artifacts in this game work which unfortunately detracts from the PDF as a whole.
In conclusion STALKER - The SciFi Roleplaying Game is, despite its mechanical flaws, still worth picking up for its amazing and detailed setting which could be run in a number of other systems.
[4 of 5 Stars!]