I haven't read The Scar yet, Andrew - but I've read quite a bit of China Miéville's other work and works - and I have to agree one thousand per cent with your opinion. As far as I am concerned, he is one of the great living authors in the science fiction genre - and, additionally, the quality of his writing qualifies him as one of the living masters of the English language.
For those not familiar with his work, a minor caution: often his writing, his story-telling, his characterizations and, indeed, his world-building... can be on the thoughtful - complex - and for some, dense - sides. It's good to keep that in mind for some (though definitely not all) of his works.
Thanks for mentioning The Scar - it's been on my want-to-read list for some time and now it's inching its way closer to the top.