I haven't read The Scar yet, but Perdido Street Station is nothing short of brilliant (and Miéville's debut, King Rat isn't too shabby either, though it loses a little by not being a 'New Crobuzon' book), so I started Iron Council with high hopes, and wasn't disappointed. It has to be said, though: Iron Council isn't as mind-blowing as PSS. It's not that Miéville has lost his capacity to fascinate and compel (and it certainly loses nothing in the imagery stakes, with its central conceit of the never-stopping train, its passengers and followers laying tracks before it as it travels ever further) - but somehow Iron Council seems less vivid, and less fully-realised.
It's as if, in stepping out of the sprawling dystopian city-state of New Crobuzon, Miéville stumbles because he's forced to quite literally cover too much ground. Much of the joy of PSS comes from its denseness - the way in which Miéville dwells on the details (and even then things occasionally seem to come out of nowhere - the emergence of the handlingers and their doomed aerial combat with the slake-moths, while a bravura, indelible feat of imaginative writing, is a prime example of that), giving the city an endlessly ramifying, pulsating life and really creating a sense of scope, goes a long way to justifying the comparisons he draws with Mervyn Peake and Gormenghast. Here, though, there's not quite the same denseness of evocation - much of the narrative takes place in the badlands outside the city, and both those parts and those set in New Crobuzon suffer from not being as fully developed. Moreover, in Iron Council, Miéville focuses more strongly on the story's protagonists (I initially wrote 'human interactions', before realising that while Miéville's characters are all people, they most certainly aren't all human), and there's a pretty clear - though not too distracting - political subtext.
But in some ways, the whole previous paragraph is just quibbling. I wasn't thinking any of those things while I was reading Iron Council - they came to me afterwards while I was trying to work out why it hadn't impressed me as deeply as PSS. Above all else, Iron Council is a great read - like all of Miéville's writing, darker, grimier and more uncanny than anything else I've come across in contemporary literature.