Un Lun Dun by China Mieville is like all China Mieville books (Perdido Street Station, The Scar, Iron Council): too long, takes ages to get going, but once it does get going it sweeps you along and you find yourself hoping your train gets delayed so that you can read a bit more.
It feels about 200 pages too long, but I can't quite work out which parts you'd cut out. The story doesn't get interesting until about page 125, but you can't get rid of those pages because the rest of the story needs them. The first part of the book is there to make you think the story is of a certain kind, so that your assumptions can be shattered by the rest of the book. Judging from some of the other reviews on LibraryThing, a lot of people don't make it that far and give up on the book. Which is a shame, because the rest of it is a cracking, highly imaginative, thrill ride. It's got ghosts, flying buses, umbrellas, milk cartons and martial arts bins. What more do you need? It's meant for kids, but I loved it.