This is the most purely FUN scenario that I've ever played or GMed, hands down. It's a once-in-a-lifetime treat for any GM who wants to unleash both his inner Cryptkeeper and inner ham. My experience with it suggests that played just right, this scenario can genuinely immerse, move, and thoroughly unnerve a group of players (even in a busy public room with full lighting). If you can manage a couple of convincingly scary voices, you should practice slipping into/out of them seamlessly!
It was also helpful to start the action in Mendev: getting there in other Season 5 scenarios has been pretty tedious. We can probably assume that under the circumstances, the Lodge and the Crusaders have established a mostly-secure series of stationed, policed roads and water routes.
Now the drawbacks (spoilers): some of the encounters are confusingly written, and have unclear conditions. Mapping the reconstituted labyrinth proved nearly impossible; once its illusory nature became apparent, it wasn't clear whether the party could simply ignore it, walking around the real wall remnants as needed and rendering the maps pointless. The scenario alludes to "creatures" in Karsos' maze, but doesn't actually describe them. Worse, though, it doesn't mention at what point Karsos attacks, or how a fight actually plays out in combination with the labyrinth and his Phantasmagoria ability--the directions were so opaque that I had to simply let the illusion peter out, and stage the fight out in the open.
Also, the party is far less likely to get the "Acquainted with Aslynn" boon that the author seemed to think: using the chalk seemed like an obvious case of "poking the unknown scary thing with a stick," and even halfway wary players were powerfully disinclined to try it. Moral: if it leads to some sort of boon, it should probably be something that a party has vaguely realistic reasons for doing/attempting.
