You can't really play Rogue Trader without this book, and I dare say it adds a lot of depth to Deathwatch, Only War and Black Crusade as well, if you want it. This is hands down one of the best books of the line, and thoroughly recommended.

This is a solid book, and probably close to indispensible for the gamemaster running an exploratory game, as it allows both the random generation of planetary systems and encounters and of strange devices and equipment, including archaeotech. A simple roll on one of the charts in this book can spawn a new scenario without constraining everything to arbitrary gamemaster decisions, which might make a lot of systems come up extremely similar.

There are three reasons why you should get this file:

1. It contains many useful ideas and materials, both for GMs and players.
2. It is free.
3. The files are available for download separately on the PP website, but downloading them separately is both a hassle and problematic because many of the separate files on the PP site cause pdf readers to crash (except for adobe reader, which is slow but doesn't seem to have any problems).

Firstly, it should be noted that the rules errata of the printed version have been rectified in the PDF version. The spelling errata, not always.

That being said, the ruleset is easy to use and the book is lavishly produced; Privateer Press's tabletop past shows in the wording of the rules, which tends to stick very close to the rules wordings in the Warmachine and Hordes games, but I would consider this a bonus, since the clarity that Privateer Press has aimed for in their wargame rules serves the rpg system well, too. It might take a little getting used to for role-players who prefer to play a little more loosely with the rules. The world of the Iron Kingdoms is a well-thought out steampunk setting, and the possibility of using Warmachine and Hordes materials as sources for the role-playing game is definitely a bonus.

Rules-wise, the system also offers a pretty unique take on social skills, which appears irritating at first, but does make sense after a while, and is actually a refreshing new approach.

The 3rd edition has both streamlined and clarified many aspects of the original Earthdawn rules, and with the alteration to the Discipline rules even player characters following the same Disciplines can be very different (e.g. it is now possible to play either lone wolf warriors or expert leaders and tacticians, depending on your choice of talents). The rules for multi-Discipline character and thread objects have also received a great overhaul.

Also, while the previous editions of the pdf file used to have (un)readability issues on tablets and non-Adobe pdf readers, the current version (available after 20th April 2012) has cleared up these issues and can be displayed without problems.