In a similar way to Elves of Athas, Thri-Kreen of Athas expands on the player character insectoid race to provide a rich smorgasbord of background materials and roleplaying opportunities for both players and dungeon masters alike to feast upon.
The background materials commence with an in-depth analysis of the psychology, physiology and biological nature of these insect creatures coupled with their basic mentality -- clutch, pack, and nation. This, combined with their daily "hunt" mentality set this race apart from all others on the planet.
Much of the middle of the book is taken up with rules. Clearly these are not present day Dungeons and Dragons rules, but they can certainly be adapted if a Dungeon Master has the time and patience to do so. For instance, there are some easy ones to consider such as the innate ability of Thri-Kreen to perform large leaps thanks to their powerful legs. This would be easy to translate. Their antennae however, is open to some amount of discussion and interpretation as to how they should be handled (blind fighting analogues being more obvious).
The final few chapters of the background deal with the nations of Thri-Kreen, ranging from those that have settled in to the human cities (e.g., Raam and Urik), to those who belong to the scholar group of Kreen. This gives a good set of divergent ideas to any player to run with in order to better characterise their character. Along with some NPCs, a fold out poster, and a genuinely interesting and intriguing (plus open ended) mini-adventure called the Taste of Fear, this book has a lot of materials inside its pages, including possibly expanding beyond the known regions of Athas that have already been documented elsewhere.
All this said, none of the materials in this book are necessary for playing Thri-Kreen or for Dungeon Mastering them. The core game materials are enough, and enigmatic enough, that players should feel very content with them. However, for the dedicated Dungeon Master or player, this is a rich gold mine to be used widely and freely. As such, I'm giving this tome a mighty 4 out of 5 stars. Very enjoyable. But by the same token, very highly specialist with no real need to purchase it.