I had a lot of fun with the Shackled City path, but I'd definitely recommend 6 rather than 4 player characters. The setting has a lots of NPCs that are great for drop-ins during the campaign, and lots of threads that are foreshadowed before being revealed in full fruition later in the game.
I let my Dungeon sub expire right as the AoW AP was coming out. I liked the first adventure, and would definitely buy it if/when it comes out in hardcover. From what I saw, it started out just as deadly as Shackled City.