This is one of the better Adventure Path books I've ran or read. There's a clunky introduction with a carnival troupe that never shows up again (I'm also not entirely comfortable with the troupe of "freaks" presented), though the investigation and battle can be interesting depending on the group.
The second section deals with an investigation into the Beast's crimes overlapped with a dungeon crawl you can complete over the multiday investigation period. It's a comfortable time limit, with enough time that you aren't in huge danger of failing, but not enough time that it's a pointless addition. The actual areas and court room scenes are interesting enough, though the haunted town can get into rinse and repeat encounters that are either tedious or deadly depending on the group.
The dungeon crawl is solid with nothing especially deadly or weak, though unfortunately there is little writing on what would happen if you tried to instead resolve the situation diplomatically. It expects the PCs to realize evil is afoot and simply raid the compound.
After the trial, it leads into a much larger dungeon. The first part is fine. The encounters are interesting, but the maps are wrong (Most of it should be twice as larger but not all of it) and there are a lot of empty rooms with flavor but little in content.
The glaring flaw in the book comes in the last section of the dungeon. First of all, all of the doors are barred requiring dc 28 strength checks. The writer thinks enough to give you a magical item to bypass the doors, but even with the magical item you would need to roll a 19 on the die with it at full power, and the item has charges. Once you break past the FIRST door you enter an entirely flooded dungeon. Everywhere is difficult terrain and if you are size small you have to make swim checks everywhere. The first two encounters in this section are behind traps, though the traps are not themselves deadly unless you have a player wearing heavy armor. The problem is that behind one of these traps is TWO high level swarms. Underwater. That can do both ability damage AND drain. My group had a pyrokineticist so could at least do infinite cone attacks, but even those would require very high caster level checks to get past it being underwater. I decided to just ignore the encounter after the first round when the crossbow user took dex damage and drain.
There's also an encounter with a near invisible basilisk that could easily end the game before anyone can react. I removed that one as well. To top it all off, almost every encounter, and room, is completely avoidable with no loss of loot or story.
The final mini-boss and boss are fine, though the final boss can be especially deadly with the wrong group or tactics. It seems perfectly survivable as long as the GM uses the exposition NPC nearby appropriately.
This would have been a 4 star book easily if not for the flooded section.