I think it really needs to use the city, not just dungeons set in the city. Rival battling power groups are important - think Romeo & Juliet for a good model. You want duels in the street, roof-top assassins, bands of thugs lurking in dark alleys, that kind of thing. The city itself needs a starring role, so design with that in mind.
The first two books of "Curse of the Crimson Throne" do a good job of this, with lots happening in Korvosa itself.
Opposing groups can be:
Churches & cults
The City Guard
Rival sorcerers or mage guilds