Lankhmar: Savage Tales of the Thieves Guild is one of the best city adventure supplements I've read, and can be used in any high-magic city. I think my only criticism of the adventures is that they don't expose the gamemaster or players to anything particularly unique to Lankhmar or Nehwon. Still, not only does the supplement have a good variety of tales, but the adventures should give a gamemaster an idea of how to use a player's guild to hook the party into a scenario, as well as what subterfuge various city factions can engage in -- with the player characters as pawns and peripherals. Several of the adventures include additional mechanics for various thief and city situations (eg. heists, demagoguery). The supplement itself is about one-hundred pages long, with fourteen scenarios. I liked three of them in particular.
The Crimson Barge: The supplement calls The Crimson Barge a "sandbox". Specifically, the Thieve's Guild has declared the luxury ship's maiden voyage fair game to guild and non-guild thieves, as an demonstration to its owner of how valuable the guild's "protection" would be. The adventure presents several very colorful characters -- including other thieves -- leaving the players to plot and plan their way to riches, mischief, or even hobnobbing with nobles and merchants. A rather unfortunate event occurs (hint: maybe the ship's owner should have sailed the ship on a test run), adding a bit of chaos to the players' plans. As a one-shot scenario, though, a game master may have the players play the colorful NPC's instead of their own characters. Also, this scenario is suitable for players as nobles and mercenaries who have been hired for the night. Depending on the demands of his players, a gamemaster may need a fair amount of preparation, or can improvise much of the adventure.
Hammon Heist: More than an adventure, this scenario contains useful rules, guidelines, and advice to a GM running a heist scenario, where the characters gather information to break into a stronghold, as well as the actual break-in -- and things that can go wrong! Additional rules add the "Heist Benny" to reflect how the characters may be prepared in ways the players overlooked (eg. spend a Heist Benny to have some meat to distract the guard gods!). The scenario itself has a magical McGuffin that's an amusing plot twist in its own right.
Scrolls of Eximir: Less of a Guild assignment than an adventure, Scrolls has the players encountering Eximir, a slightly batty old wizard who thinks he's already hired the party to retrieve a set of scrolls from his own temporality-displaced wizard's tower. The tower consists of several rather creative and dangerous encounters, implicitly encouraging the gamemaster to add his own strange ideas to the adventures. Amusingly, Eximir comes off as a bit scatty, yet is as powerful as Sheelba and Ningauble. He should make an amusing (if unwanted) patron!
The adventures are remarkably concise -- no encounter padding here -- but the limitation of space means many of the adventures are pretty linear. Players may need to spend bennies to succeed in a roll or the adventure halts. The gamemaster should expect to improvise to guide the players back to the adventure, or develop any alternate plans the players come up with.
Often, an adventure will have the players make a roll to see if they recall a rumor or other important streetwise information. One suggestion for these adventures is that, instead of this, the gamemaster prepares rumors or whatnot during one adventure that will be useful in another. The PDF format of the book allows a gamemaster to print out whatever pages have a rumors, cut out this information, glue them to index cards, and hand them out during the campaign.
Also, just for fun, if some players are running late, the gamemaster can roleplay out a prologue. Players act out the Guild higher-ups deciding among their guild members whom to select for a task. They eventually settle on the player characters (particularly those associated with the players who are late), citing notable qualities such as "expendable", "owes me money", and "stingy with donations to private funds".