Ahhhhhhhhh, excellent, thank you!

I was so confused when I saw the Leviathan boxset which had that Tyranid force but no genestealers which I always thought was a huge part of their force, and then when I saw your Genestealer Cult post they didn't seem to be in any of the photos either. So, thanks for clearing that all up for me. I'm really glad they're in both armies. I just love the simplicity of the motivation of these armies... to eat all biomass. I didn't know the backstory of the Genestealer Cults, but it is a very clever way to add some mystery and intrigue to such a simple motivated race.

I assume technically there might be Genestealer Cults of Aldari or Orks or Tau?

I've been really enjoying all the 40K Eisenhorn books by Dan Abnett and I think I'm on the last one. They are the first and only 40K books I've read. Is Sin of Damnation a good next one? Or should I start with a different series and work my way up to that one?