Let's make a clarification about the topic: Out of the Abyss is probably the best adventure published for D&D 5th edition.
I had many pleasant hours while running it and this post wants only to point out what are in my opinion its few minor flaws.
Hopefully it will be helpful to those DMs who are planning to run it.
The extreme and bizarre environment is a strength (you see and meet funny, strange and exciting people and places) but it's a weakness as well: it's an extremely dangerous environment, sometimes too much dangerous, and too often the interactions with NPC creatures is more limited than that in more conventional campaigns, because most of them are hostile creatures or too much "alien" and diferrent to properly communicate with the PCs.
Party is going often to move and act in narrow passages and small places, and many NPCs will join the group.
Therefore in combat situations a kind of "traffic jam" will be likely, making difficult manoveurs and actions both for the party and the opponents.
Again it's very funny (in my campaign a lot of interesting situations started from the madness of a PC) but when indefinite madness happened the party had to stop its plans and start wandering the Underdark, looking for someone who could heal the mad PC.
The party was more troubled also because it lacked of a proper Cleric.
The party id going to move and move again in an area as big as the Sword Coast. It means travels of weeks or months and in the end I tended to skip the travelling parts or I gave it the chance of teleporting to the right destination.
I like maps a lot. They help me focusing better on the place and handling scene and situations sundenly created by unexpected PCs' actions.
I found maps in the books to be too few.
I'd liked more maps.
Those are in my opinion some maps that would have been useful:
Derro's Quarter in Gracklstugh
Tower of Sorcere in Menzoberranzan
Tower of Araj
Some areas of The Filthriddens and The Labyrinth.
Despite of these minor flaws I strongly recommend to Out of the Abyss because it will give you many funny and pleasant gaming hours.
Let me know what you think of it.