Heh, here I am. I have indeed read Mieville's debut, King Rat. I like it quite a bit - it doesn't have the scope and fecundity of the Bas-Lag books, but it shows Mieville working his muse in a different setting - modern-day London, and is a valuable indication of his breadth as a writer, I think.
I love reading books with a strong sense of an urban environment or environments - whether it's a purely imaginary metropolis, like Harisson's Viriconium, or a series of deftly sketched and imaginary cities, as in Calvino's Invisible Cities, or a real world city as in Moorcock's London novels. Like the last, this book takes London itself as its setting, and then unleashes the weird into that context.
It draws from popular folklore, parlaying the story of the Pied Piper into a strange tale of hybrid animal/humans, a plot by the King Rat and other animal Kings to finally have vengeance on the Pied Piper, a direly clever plan by the Piper to enslave the people of London with his music and in the midst of it all, the perils of one young man, half-human son of the King Rat struggling to come to grips with his own identity and cease being a pawn in this game.
The rhythms of drum-n-bass music run through this work, as do a deeply convincing picture of the grimier sides of city life, the cheap takeaway noodle meals, the beggars and tramps, and most of all the sewers. Mieville literally drags us through the London sewage system in this book, so it may not be one for the weak-stomached!
As with any Mieville book, some of his inventions won't sit well with everyone- I myself found the notion of a rat-human hybrid a bit hard to swallow, but once you decide to suspend disbelief, there's a great story here, that works well on the level of characterisation as well.
I love the epilogue, with the young man's admonition to the rats of London to 'put the rat back in fraternity'. Really cracked me up.
Mieville has stated that he may write more works in a real-world setting in the future. That certainly seems like a good idea, on the strength of King Rat.