Just ran this for my [mainly] adolescent group and they firmly enjoyed it. We're in the middle of fighting the "no spoilers" boss but they are all really enjoying it.
The amount of suspense seemed to be just correctly balanced, for my group at least, with a good springboard to other adventures (as well as the recommended sequel). Just the right amount of fighting and suspense.
Detective work and "dungeon raiding" is the call of the day - though there could have been more of the "dungeon raiding treasure rewarding" disperesed throughout the adventure instead of bulked up at the end (seemingly only a minor criticism).
On the note of criticisms, there's not many. Maybe more traps? (our Thief spent the whole time trying to roll "that trap-checkin d20" in every single room and every corridor), also a little more loot could be smattered about? But for a Thieves' Guild a GM could simply throw some things in here and there to suit without too much problem.
The few traps that ARE in the adventure i, personally, like as the creation/placement of traps i consistently struggle with in creating adventures so i found them useful and the group had unexpected fun (the minute the Thief dropped his guard, well...). To be clarify: they're not novel or complicated; i just hadn't thought of them before so much fun was had.
Another criticism by the players was they felt it kind of "empty", but i feel it added to the suspense/horror. The players agreed once this was pointed out.
Conclusion: very much fun was had. The players enjoyed playing it a lot more than i would have guessed simply reading through the adventure during prep. Some minor typos and maybe a few more encounter/traps, depending on the amount of suspense/action you want, but all told it was certainly worth more than the paper it was printed on.
I'll certainly be keeping an eye out for more little adventures like these from this author. Consider giving an extra penny or two - you'll get your money's worth for sure.