I have only just recently read
Snow Crash, and haven't read any of Stephenson's books before. I can see that it is a pretty good book, very forward thinking and original, but I do have some nit-picky criticisms that I don't think that the book addressed or resolved very well.
The fragmentation of nation states : The story calls for the world's national governments to have been subsumed by corporations and private interests. As is often the case with sci-fi, the author has taken an existing phenomenon (in this case franchise stores and restaurants) and scaled it up. Yes, I can understand that this was done in a way for comedic effect, and to loosen the restrictions on the characters' actions, but even if you can accept that such a system would be stable (it would almost certainly be more like lawless anarchy, in my opinion), it seems like a bit of a cop-out to have these "franchulates" being operated by sketchy caricatures of big organisations (e.g. the Mafia). Also, surely it would be more likely for the different franchises to consolidate and be less apparent to the man on the street.
Hiro's back story : OK, so Hiro Protagonist is one of the creators of the metaverse, and yet he lives in a garage, and does quite menial jobs... hmm, I guess there are enough instances of similar things happening in real life, it seemed a bit incongruous.
The Rat Things : We are given the impression that no-one outside of Ng's organisation is aware that they are dog cyborgs. Yeah, like that's something you could really keep quiet.
When is it set again? Hiro and Raven's back stories suggest that the book is set around now (200x) at the latest... but we have major changes like some of the plot devices mentioned above and they have become accepted ... I don't think that even in 1988 Stephenson could have reckoned that so much stuff could change in such a short time. Still, I guess that's what fiction is all about. And I guess that the Metaverse predictions make up for it, if you're keeping score...
I could go on (about Snow Crash, and Reason, and the Raft, and the whole Sumerian thing...) but the beauty of the book is that this would just serve to make me look bad.
IRT Azzer: But the 'franchulates' are too fragmented and specialised to be effective platforms for governance. The other difference is that in 13th C. Europe, there were still major national state interests (such as kingdoms, and the church) inside of which the city-states operated.