It's taken me four days to read Philip Reeve's A Darkling Plain
which in some ways tells you everything you need to know. I ripped through the other three like a traction city through wheat.
In this book the Tractions Cities make their last sortie on the Green Storm. The Green Storm is riven by rumour and feuding, Tom and his daughter Wren Natsworthy change sides a few times (because as traders they aren't really "on side" at all); Tom's wife Hester walks through the word with the Stalker android, Shrike, and Little Fishcat, an orphan boy, accompanies the accused Stalker (once Anna) Fang. No one seems to have very strong motivations, which I suppose is a reflection of real life, but it is confusing.
But the real problem is that the very things which created such awe and wonder in the first book really don't stand up to the close scrutiny of the fourth. By this time we want to know how traction cities work, and Reeve just can't quite pull it off (the same problem struck Heinlein's short story, The Roads Must Roll. My criticism is about the effect of focus, not a failure of technique).
Also an issue is that Reeve's joky nomenclature and ironic prejudice starts to get a bit wearing. And its long time past that British writers went beyond the Teutonic German all jackboots and leather jacket and called Wolf.
Yet despite all that, the books still hold to their rigorous political stance--even the Greens here are eyed with suspicion--and there are some lovely bits of writing.
This is from the end of A Darkling Plain,
Shrike, the killer android, has seen Hester die with her husband Tom. He has taken their bodies and watched them disintegrate. He has slowed down and let the years go by. Now he is awake again, and the people he meets seem primitive, their metal the left overs from the age of the Traction Cities. He "imagined that their society had no machines at all".
"...but as they brought him through the town gates he saw delicate airborne ships of wood and glass rising like dragonflies from tall stone mooring-towers."