The Carrion Crown Aventure Path promises to deliver a survey of classic gothic horror tropes, and in this installment, gives us an excellent examination of Shelley's classic (which for you non-readers tells a very different story than Universal Studios did).
The story of the module is brilliant. Yes, the party is railroaded, but the road is built in such a unique way that my players actually would have engaged it without the monetary reward. By established pattern, the second part of an adventure is generally where the PCs begin to interact with the overarching story and this one brings them in strongly.
The encounters are challenging, on the whole. One early encounter has the potential to be rather harsh (this would be the one that the other reviewers complaining about ability damage refer to), but if the group has just completed The Haunting of Harrowstone (and learned even a little bit from it), they've likely developed solid tactics for dealing with this manner of threat. A challenge, sure, but nothing insurmountable.
On the topic of encounter design, I'd like to spend a moment discussing the "middle boss" fight (V&G for other GMs). Wow. If there were any one thing in print that the publishers of 3D dungeon terrain could point to and say, "Look! This right here is why you want to purchase our products!", the three-level combat, with obstructed sightlines, narrow footing, and dynamic environment of this encounter is it. Markers on a battlemat simply cannot do this fight justice. 5of5.
The story overall mixes a healthy dose of investigation into the combat however. This is one for thinking PCs who know how to fight; a pack of combat monsters who depend on the story to feed them clues will go hungry (and the design of the story allows for that, too). The fact that the party is on a rigid and unforgiving schedule throughout the first part simply adds another challenging dynamic: they'll have to manage resources in a way they aren't likely accustomed to.
The second half is also well-designed, though by this point it is much closer to a traditional dungeon crawl than the first part. Our heroes' reward for meeting the challenges of the first half is another cinematic, tough, confusing boss fight, with a very thematic and story-inspired surprise element that will challenge their teamwork in a very unique way.
If I were doing the same story, I'd be hard-pressed to come up with any suggestions for improvement. The Hergstag encounter area does have the potential to either be a TPK factory, or a repetitive tactical exercise depending on how (and when!) the party approaches it. The second part is likewise somewhat flat until the final encounter begins, but when it does, the players are likely to stop complaining about having an easy time up to there!
The first thing you'll notice is that, unlike Players' Guides for other adventure paths, there are no extensive writeups for each individual character race/class. In fact, this one manages to do that job in a few paragraphs. That leaves the remaining twenty-odd pages for the naval combat rules. At first glance, these appear solid, though of course we'll have to wait for a play session to give them a full test.