The degree of fear in the place. There was a very dystopian edge to it, that anything other than total conformity was just waiting for trouble to fall on you. It's the worlds biggest official "no fun zone". Music? Nope. Style/fashion? Nope. Take a boat out diving, or explore heritage sites in the desert? Hope you've got a shit ton of police permissions *and* that the cops are in a good mood, and the stars are correctly aligned, cos otherwise you're grounded. Until the last year or so, solo women weren't even allowed into the country, least we taint the place with sin or something stupid.
In Iran, you can, ya know... just get on a train. No biggie. Everything in Saudi Arabia was such a frikkin "big deal" and drama. Every move you make is suspicious or dangerous. Everything you do has to be scrutinised, stamped, approved, and "allowed". When they say Iran is a "prison" for women it's 90% hyperbole and bullshit and 10% exaggerated kernel of truth, but Saudi Arabia really feels like that, even as a westerner only there for a few months. God knows how it feels to be born there
I wouldn't know, because it's pretty much impossible to have any meaningful friendships or contacts with the locals, because they're too bloody scared to share anything.
It's ironic how westerners are disturbed or disgusted about the social credit system in China, yet are totally A-OK with Saudi Arabia doing basically the same thing, but with lower tech, and instead of being blocked from booking comfy seats on the train (the brutish commies!), you get tied up in public, and flogged until you're half-dead instead (good law and order policing!). Iran also has corporal punishment, but nothing like the enthusiastic dedication to it that the Saudis have, and nothing like the creepily over-extended surveillence state of crazed religious nuts spying on every tiny little thing every single person does 24/7. You'd have to do something fairly blatant and in-the-face of the govt in Iran to seriously piss them off (I used common sense, but was never especially cautious, and never reached the line). In Saudi Arabia, trying to buy a can of drink at the wrong time of day is enough excuse for a good kicking (for reals - I actually saw this happen to some poor sod).