the little black books it probably has the most iconic and recognisable graphic design of any rpg.
Agreed.
the rolls enable a lot of action if the players keep things moving.
The rest of this post is a bit of a ramble that was prompted by your comment.
I'm hoping to get in at least a little bit more Traveller GMing experience. To me it feels like there are two main demands on the Traveller GM (hopefully not generalising too gratuitously from a limited experience!):
(1) Making the system (ie 2D + DMs = target number) work properly, rather than just be a ritual covering for GM fiat. My mental arithmetic is pretty good, so my real-time sense of probabilities and numerical distributions is OK. Remembering past rulings and being consistent with them could be trickier, though - the rulebook says that the GM should write these down to establish precedents and house rules, but in practice I'm not that organised (not even at work half the time, let alone when engaged in a leisure activity!).
One example that I came up with in the session, and that I do remember, is making a check to find a broker: 2D + Admin, with every full 3 (ie 3, 6, 9, 12) allowing a broker of 1/4 that degree of skill (ie broker 1, 2, 3, 4).
The rulebook does have some of this sort of stuff - the social interaction/bureaucracy stuff, and some rules for repairing broken-down vehicles, and some other vehicle and vacc suit rules; and of course the trade stuff - but over time I think you'd want to build up more of these sub-systems to help support the system's connection between skill levels, action declarations and fictional outcomes.
One interesting feature of the systems that are in the rulebooks is that one skill level isn't always just a +1 (eg for many Admin checks it's +2 per skill level; for many Vacc Suit checks it's +4 per skill level; etc) and I think good GMing would require keeping that possibility in mind for these house subsystems too.
(2) The other GMing demand is managing the fiction. In itself that's obviously not unique to Traveller - but the demands from SF are (at least for me) different from the demands for fantasy, and require maintaining something where all the implied setting (which I think is very rich as per my OP) is kept together, and the action keeps moving along at a nice pace. The animal encounter subsystem, and the trade goods subystem from Book 7, are two examples of what I have in mind - the rules give you abstract results, but as GM you have to clothe them in SF colour/flavour.
I didn't have to do any animal encounters in the session I GMed, but if the PCs go out in their ATV then this should come up. I did have to do trade, but thankfully the player worked out what the goods were (ambergris, or something similar, from deep-sea creatures - I was able to add that it was harvested as a by-product of research, and that it was valuable because only these fairly high-tech researchers could get so deep into the world's oceans) and so I didn't have to work it all out for myself.
I think this aspect of Traveller seems to really support a high level of player participation in the content generation/specification process (both to take some of the burden off the GM, and to help ensure a genuinely shared conception of the gameworld) - as Book 3 seems to suggest, and somewhat at odds with 80s/90s RPG orthodoxy.