I unfortunately have to disagree with Keasar. I bought this one due to the fact, that it was considered to be extremely lethal. My players enjoy challenges, consider most scenarios to be too easy and I am a sucker for well-crafted enemies.
I'm in a similar situation, but my experience has, unfortunately, been different from his.
This adventure, unfortunately, only features one well-crafted thing, and that is the Boss. The premise is ridiculous, the story consists of plot holes and I had to spend about two hours making sense of the background and rewriting it. Even after that, I was hard-pressed to fight with the suspension of disbelief. The final Boss was cool and a challenge, the rest of the encounters screamed "Fireball Formation". Not as bad as "Eye of the Crocodile King", but quite close.
A for Creature, F for the Rest.

This mod has well constructed encounters and opponents that actually provide a challenge. I find 90% of the pathfinders mods as easy and provide no challenge to my group.

The story is linear like all pathfinder mods and has a simplistic story. I am fine with that because the mod was actually challenging. To be honest this is what we expect from Pathfinder mods. The authors are limited to 12k words per mod. You are not going to see very good stories until that is increased.

Ooh, where to begin? A subpar dungeon crawl. Monsters with "neener-neener" tactics and abilities and a final encounter which is simply overwhelming due to the boss creature's à la carte menu of "you die" abilities.

If this were in print it wouldn't be worth the paper it'd be printed on.

"Hi, I'm your venture-captain. We have a rat problem in our basement. Go kill everything! Also our senile janitor says there's an ancient evil down there, so be careful!"

And that sums it up. The senile Bossell is a stupid excuse for this "plot". The combats are either too easy, tedious, deadly, or downright superlethal. I honestly don't have anything good to say about this scenario.

If you like mindless dungeon crawling with no roleplaying, no plot, and no idea, this is the scenario for you.

When I ran this for a table it seemed pretty rough. Too many story elements didn't make sense and one thing on the map still baffles me. If your players actually try and figure out mysteries don't run this one. Most of my prep time was spent repairing holes and filling gaps. It ran well at the table with players challenged by the settings as much as the monsters.
As I say in many post don't play up in PFS scenarios or you may get a TPK. No matter how easy the first few fights go resist the urge.