This is a complete campaign in a very readable book. Bruce Heard takes the concept of a flying circus literally, and created a fantastic world within the Calidar campaign. The book is richly detailed, and very easy to navigate through.
While I am not knocking the larger Adventure Path compendiums in any way, Dreams of Aerie is able to accomplish many of the same things in a more compact format. I would compare this book to some of the late 1980's TSR Compilations such as Temple of Elemental Evil as far as taking characters from one stage of progression to another without trying to take you all the way from level 1-20 like the current Adventure Path format attempts to do.
Dreams of Aerie does have a plot, and several NPCs to drive said plot, but there is plenty of room for the game master to tinker away to customize as they see fit.
The generic system Calidar uses should be easy for most DMs to convert to 5E, Pathfinder, or other systems. If you're tired of dungeon crawls, but aren't sure you want a true city campaign, this a great option for you.