I'll admit it; I'm one of those who didn't give this one enough credit when I first saw it. "Oh goodie, cultists summoning something with tentacles. I get enough of that in our two-year-long Call of Cthulhu campaigns..."
You know you've been thinking it too. "I'm sick of judging combats with tentacles!"
Please hear me out.
I see very few people in the G+ communities talking about running this one, which leads me to believe that many others are judging books by covers and falling into the trap of viewing only the basic premise.
Or, to be fair, it could be that it's not a new release. Or that you didn't find the cover art stunning at first glance. Or you might just not be into the "cultist" scene.
Seriously, shed those reservations now.
One-shot vs. Campaign?
This has a lot of meat to it. A LOT. It's not going to play nicely as a one-shot unless you condense it to a few key encounters -- which, actually, could provide for some high-quality play. I might try that for our next game day and/or mini-con.
Conversely, if you're running a campaign and you read this module ahead of time, there are tons of hint you could start dropping. Or, if you're like me and hit a wall during the campaign, you could find yourself picking this mod up, gritting your teeth against the "trite" concept, and coming up for air a couple hours later armed with pages of notes and a maniacal grin that worries anyone you live with.
As I mentioned previously, the most often-encountered foes harken strongly to the Hollow Ones found in the core rulebook, which I ran as part of a huge, multi-session, crescendoing scene in the sandboxed village, Port of the Black Pearl (formerly the small shanty town from which Tower of the Black Pearl kicks off). The party still isn't sure if the faceless men with things spawning from their midsections were creatures that had been summoned, or if they'd been working alongside a coven of witches, so it made perfect sense to play on that bit of mysteriousness: The eyeless acolytes in the Pit are now faceless, albeit wearing robes in a different method of color-coding. [Note to self: Do not allow faceless creatures to become a crutch just because a judge doesn't want NPCs to be able to answer interrogations.]
Summary: Even if you've only skimmed it, it's worth taking a good cover-to-cover look -- or at least check out the 3rd level, and the intricacies of travel within. There are still plenty of other monsters besides cultists, and I could see reworking a good portion of this place to be run by the mineral mining critters instead of humanoids...even with no huge threat in the pit itself.