Hailing from Scotland, Graham McNeill narrowly escaped a career in surveying to work for Games Workshop as a games designer. He has a strong following with his novels Nightbringer, Warriors of Ultramar, Dead Sky, Black Sun and Storm of Iron.
Much like the Daemonhunters Codex at the time, I thought this was a great addition to the Warhammer 40K game. The opportunity to make model conversions was still a big part of the hobby and this book did provide encouragement for this with the Inquisitors and their henchmen. I had a friend who was a big time Sisters of Battle fan and he had a pretty extensive army. He was definitely grateful for the options that this book provided at the time (though I think he still lost more games than he won). Faith Points were a cool mechanic (I think they were in the rules and Chapter Approved update before this) and I think it was a way of giving the Adeptus Soritas army something that made them stand out.
Oh emperor how I adored this and the Demonhunters book. As a huge fan of the novels that took place in the Inquisition (the Eisenhorn novels specifically) the ability to play with individually kitbashed models representing characters you thought up was amazing. Also this was the first and much needed introduction to the Sisters of Battle which has been a popular faction ever since. At least in my area.