A really good-looking city mission featuring nice variety of locations, with the underground hideout areas worth particular praise. Perhaps nothing especially original in this one, and its story quite forgettable, but both the brushwork and the atmosphere are very good.

For all the rest, it depends on what style of play you prefer. City missions have generally fallen into one of the two categories: exploration-based, mostly open and accessible maps in which you are usually free to choose your own way (think The Sound of a Burrick in a Room, or Midnight in Murkbell), or maps divided into several distinctive sections in which you must go through a number of predetermined checkpoints to progress to the next section (think Rose Garden, or Endless Rain).
Whispers Below the Cobblestone, unfortunately, falls into that second category. Personally, I'll probably never understand why you would prefer such a limiting map design philosophy for a Thief game (one of the biggest flaws of Thi4f for that matter). It could be somewhat justified in a detective-themed mission, but that's not the case here.
There aren't any more major sins that I found, save for an occasional quicksave tournament here and there, characteristic of missions with lots of verticality.

It's still worth playing, nevertheless. Many players seem to enjoy this particular type of gameplay, so it may be just your style.