This is a sequel to his Thunderer. I do recommend reading that first. Since this one starts out with the main character amnesiac, it's not obvious up front, but it becomes obvious.
Now, Thunderer took place in an enormous city haunted by gods -- strange, inhuman, numinous beings, whose apparitions were endless and quite capable of driving men mad. Although individual gods appeared generally for a period of time and then less and less until they ceased, new gods always appeared. Gave an interesting effect to the religions of the city. The plot lacked focus, I thought, and some things that proved to be important to what proved to be the main plot were introduced a little late -- but, you notice, I picked up The Gears of the City.
This one is better focused. The main character lacks his memory after an encounter with the Mountain, a stable though numinous landmark. He landed -- he can travel through space and time in the city -- in a portion of the city lacking in gods. He meets up with a prophetic lizard and with the Low sisters, and learns more of the oddities of the city. And of the looming War. Characters -- villains and others -- reappear from Thunderer in a much more elegant plot. And things -- even things from Thunderer -- get resolved, magnificently.
Despite the title, this is not steampunk. Anachronism-punk, maybe, since the characters can go through time and you get the oddest mixes of technology. 0:)