It's very good, and with the aid of comments here, I managed to gather all six of the core items, complete all upgrades with the smith, and get all the way to the Bad Moon Rising ending (which I tried with no patron and each of the three), having already done the Twilight Zone and For Whom the Bell Tolls endings. However, I can't seem to find a 15th Valac Shard despite roaming everywhere I could find with the helm, including back near the start outside the labyrinth, and trying to blow, smash, or cut anything I saw along the way.
I wasn't sure whether there's anything to do with the golden artifact in shop basement of the forgotten city, though I did try using the ring on the shade in the door on the east side of the city. There's also that concealed chapel on the surface in the west garden area of the labyrinth, and I don't remember finding anything special to do there.
Like one of the other commenters, I'd also say the waiting in the darkened maze is a solution that could use a hint. The only apparent bug I hit was one time with Limnos where the outer door (near the pyre) was shut when I tried to leave after accepting patronage, forcing me to reload an earlier save since there was no other means of escape (I have no idea what caused it, except maybe playing around on the roof of that building)
EDIT: I finally got the last Valac Shard after seeing the comment about shoving blocks. I'd seen the blocks in question and found them curious, but hadn't noticed any hint suggesting a particular arrangement. A pattern on the floor there would be useful.