Pretty good. Just don't expect any real answers.
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By Mildmannered88
"I didn't want to present anything... as any kind of definitive, objective truth. I don’t think anyone should, either... partly because, well, no answer will ever be satisfying enough for everybody. Nothing will match everyone’s massively varied perceptions of the setting... It’s Warhammer 40,000, after all."
-Aaron Dembski-Bowden, “The Master of Mankind" (Afterword)
^ If you know anything about 40k, you should already be expecting as much. Go in with that mindset, and it's a solid read.