[MENTION=1]Morrus[/MENTION]: Your article link gives me a "page not found" error. Sacrosanct's original link works for me, though. Just FYI.
The Underdark is not a happy place. Most of its inhabitants are dour, depressed, depraved, or some combination thereof. You can feel the weight of all that earth and rock above you. It can be quite claustrophobic. It's grim and dark, both literally and figuratively. And then there are all the demons lords ... Having read a draft version of this adventure, I can tell you that the whimsical characters and situations help add some much-needed levity to what would otherwise be a real downer of a campaign.