Mega Dungeons: Under Mountain or Under Enthused?

Warning: This post will probably annoy a lot of people. If you are one of those people, know that before you read this, I am not saying your stlye of play is wrong. I am posting this to express why this style of play does not suit me.  If you are having fun in the Under Mountain or other sprawling labyrinth, more power to you! But it's not for me. If you disagree, we can chat, but please keep comments civil.

Everything old is new again. Old school D&D play style has seen a resurgence in recent years. Along with the rise of OSR systems, Wizards of the Coast has also steered the new edition of Dungeons & Dragons back in the direction of AD&D first and second editions. With this resurgence of interest in the old games, the old modules and dungeon crawls have also seen their Renaissance. 

... which brings me to the "Mega Dungeon".