Darksword Adventures was originally written as a role-playing game supplement based on the Darksword trilogy. As a result, I very nearly bypassed it, since I am not interested in the gaming aspect of Darksword. After thumbing through the book, I decided to buy it and I do not regret it.
Although there is a lot of gaming info in the book, it is easy to skip. Included with the gaming information is a lot of history and explanation of magic in the Darksword world. Anyone who enjoyed reading the trilogy should find this information helpful and interesting.
This book is not essential, but if you are thinking about re-reading the trilogy someday, reading Darksword Adventures first may help to fill in some holes and improve the experience.