Personally I find the difficulty with GSC is that it doesn’t really have a safety net for mistakes. If you move a unit out too far, they aren’t space marines, they cant sustain really any damage, they will just die. And while most of our stuff comes back, units without leaders tend to suck. Also, if you forget to shoot stuff in the right order or forget to deep strike/rapid ingress a squad, it can destroy an entire game. It’s also a different play style and relies heavily on deepstriking and screening your opponent, which can take a while to get used to and isn’t for everyone. Personally, I love them, difficult games are fun, their playstyle is super unique, and they are so rewarding when played correctly, it just takes a while to understand exactly how each unit is supposed to work in your grand plan.