Finally played this.
We were 5 first timers and left the Spacing Guild out. Only I knew the rules. It was a blast, everybody was laughing histerically at the end when the Bene Gesserit player won by prediction on turn 5. In retrospect we probably got lucky in getting what seems the coolest ending possible for a bunch of Dune aficionados, specially so as the BG player really schemed and manipulated people on her way to victory.
We played the "Optional" mode (Advanced sans spice combat) as it seemed the better balance of theme-speed. We also used a couple variants:
Alternating spice blows/ single on odds, double on even rounds (felt a good balance for Optional mode, as double would hurt Fremen spice-efficiency, while single spice blow could hurt map presence and nexus frequency); and
1-pass only auction (draws favoring storm order) which again, felt a good theme-speed, as default auction can slow the game too much, and that other, even faster variant where everybody just extend hands and show at same time miss the Atreides bid/tell that gives the phase it's nuance and mind-game IMO). Oh, we also played a
7 rounds max game.
It took ~4h, in great part due to the slow start where we learned the rules. Considering we're all first timers, it felt smooth, with no phase feeling boring or such.
What would think about spice combat? Personally I'm not a fan and would prefer keeping Optional mode, but in name of fairness next time I'll make sure to explain my friends the spice combat rules, discuss it's pros and cons, and go with whatever they decide. Who knows, maybe I change my mind about it.