I ran this today in a kind of a continuation for the FS1 - Fortitude Dungeon. While not quite as good as the FS1 in comparison, it was a fun little adventure in itself.
The beginning, I feel, is a little too split. The two hooks, while nice, are both compelling enough not to stay to listen for the other. I tried to slip them both into my game and bring them up naturally to the player, but I only had time for one as after that the player immediately set off to find the adventure before I could really deliver the other one. Perhaps they can be delivered both at the same time without monologuing the opening speech, but I didn't manage it. Also some additional pointers for how to find the Tabernacle without holding the player's hand and leading them there would of have been appreciated.
As for the dungeon itself, the only thing I'd say is getting some more variety in the enemies offered. FS1 had a number of different enemy types and in comparison this had clearly fewer. Something different in the mix would have been nice, or even with a greater mix of weapons. For low hit point characters even a club or a stuff can be deadly, which was less of a problem with FS1.
On the other hand however, the dungeon itself was quite nice as was the way enemies were located. I especially liked how it was noted how certain types of routes would lead to chances of surprising enemies, which is quite crucial for a thief, and in my case, mage / thief. The dungeon itself was considerably larger than in FS1 with greater amount of truly threatening enemies moving around. The spacing of the enemies was also good. Offering both chances for quiet assassinations and (for my player) dreaded straight up combat.
At the end of the adventure the player had managed to somehow survive, despite some very scary situations. The session ended with a good mood and the lust for adventure had been sated!
As for the true solo section of the product, I have not really looked into it as it was not the reason I picked the adventure up.
All in all, I would not hesitate to run this again. It was a solid and relatively quick (we took about 5 hours with it), one session adventure for a lone PC. Tho again I'd recommend straight up mages to exercise extreme caution!