I will admit going into this module with somewhat low expectations (not a fan of pathfinders firearms rules or their take on steampunk) but even then I was underwhelmed.
As previous posters have stated it's a long dungeon crawl with low RP, steady combat slog and a somewhat paper thin plot. Now it does have some unique creatures to encounter including my favorite 4-armed creature in significant numbers the tactics and usage of most of the opponents doesn't seem effective for high level play.
On the crunch side I was hoping this being the first official module with gunslingers in it would be a good example of how to handle them in a standard game but that was the weakest part of the setup. None of the common gunslinger builds where in evidence and most of the gun using opponents seem to have gone out of their way to avoid the feats/attributes that makes guns dangerous (large sized creatures with dumped Dexterity and no fast reloading or feats to increase fire rate or damage).
Overall I have to admit a serious disappointment with this module. I expected better.
Having recently run this module for a 5 player PFS game I must say it was extremely entertaining. My players ended the session raving over the challenge of taking the castle and cringe at the sight of certain colored hats now.
I wound up with a party that was at the top end of the expected APL for this module at 5th so where able to power through some of the more difficult challenges (3rd level spells tends to make the goblinoid encounters a LOT easier to handle). Keep that in mind if you do run this and personally I would have preferred to add 1 level to all the fort NPC's to make them less 1 shot-able.
Personally I found the fort challenges reasonably well designed and straight forward to run and are likely to keep everyone entertained. The underground areas were less challenging but some were significantly more memorable (I'm looking at you the previously mentioned hat wearer).
Overall I only have 3 areas where I felt things where a bit less then perfect.
Final encounter, the bosses abilities are way to swingy, everything relies on a single target save. Honestly they were no challenge at all to a party that made it past the Barrowhound. I'd re-do it with a few less enchantments and more summoned servants.
The goblinoid opponents where entirely too easy to kill. I know they outnumber the PC's significantly but with as low of a to-hit and HP's they have they could barely touch most of my melee PC's and died after 1 good hit.
The map, as beautiful as it is the layout on the grid is pretty confusing. Most corridors are not 1 square wide and are usually some mixture of 2 half squares shoehorned together. If there had been clear lines for the major passageways instead of a off-center overlay on the grid would have really helped.
Anyway, so far this is still one of my favorite modules ever and I can't wait to see what this author does next.
Ran this for my local group at the High Tier (8-9) and must say by the end of the first encounter half of them where thinking of fleeing the manor.
The combats were interesting using opponents we rarely get to see and the RP opportunities were plentiful and pleasant (for me, the players hated everyone). It was a little long for a standard 4.5 hour session but that's the nature of sandbox adventures.
The only problems I had with it was the final challenge was a bit of a letdown challenge-wise and the guidelines for completing the actual mission is pretty vague and difficult.
I enjoyed it and look forward to running it again.