The ambush mechanic was a bit of a pain and contains the possibility for a series of bad PC rolls (and high GM rolls) to end the adventure with them solely on failed stakeouts. While this is fine for a homebrew (as you can then move on to the invasion of Magnimar by demonic forces), it really does not work if you are going to use it for PFS play.
Other than that, however, I really enjoyed running it. There were a couple of different ways for the PCs to find the BBEG, the fights were definitely challenging and the mystery aspect of the adventure can lead to some interesting conclusions on the part of the PCs (the group I ran was convinced the attacker was coming from the interior of the Irespan ... talk about a potentially lethal red herring).
Was the final encountered overpowered? It had the potential to be for the pregens, especially if the Babau gets summoned, but for a party of 6 5th level PFS PCs this should be a close fight ... as any fight with a BBEG should be.
And the BBEG has the potential to be memorable recurring villain. I do plan on breaking this one out in a homebrew at some point simply for that purpose.
That said, this is definitely NOT a module for new players. Players should be fully familiar with their PCs' abilities; lack of that knowledge will definitely increase the death toll.
All told, I would rank this as 4 stars, but due to the ambush mechanic issue, I'm dropping it to 3.5 (rounding down for the star rating options).
