Adventures written for 1st level characters can be tricky, especially dungeon crawls in a "contained" environment (such as the Godsmouth Ossuary). However, in my opinion the author pulls it off very nicely; it's a challenging adventure for 1st level characters, but rewards and monsters are well-balanced. And even though the PCs cannot “retreat” back to the surface, the author has taken it into consideration.
The author uses a lot of cool monsters and all of them have their motivations and place in the module; I especially love that he utilizes so many variants from 'Classic Horrors Revisited' (although he originally designed them, so it's no wonder ;)). Also, this adventure contains lots of juicy details (some of it relating to Thassilonian history and the Runelords), well-written and evocative descriptions and pretty innovative hazards/traps (some of which even aren't "real" traps). What’s even more important is that none of the encounters, traps or puzzles in the module are “showstoppers” – they shouldn’t grind your game to a halt. Experienced players may find a bit more treasure, but apart from that, even first-time players should be able to enjoy the adventure and have no problems with completing it.
The backstory may not be anything new, but it’s written so well that it should satisfy the needs of both seasoned and beginner GMs alike. The antagonists in this adventure are golden; without spoiling too much I’ll simply say that rarely have I seen such tragic and complex NPCs in published modules. My favorite is probably a run-of-the-mill guardian monster from the Bestiary, who’s "eager to taste the thrill of combat once again" after "millennia of boredom". Great stuff!
The only negative thing for me in this module was the map of the dungeon; it's quite boring for a dungeon, and it's way too symmetrical for my taste. But this is a minor issue for me; I often redraw or modify maps in published adventures anyway.
I can heartily recommend this module to all Pathfinder GMs, beginners and veterans alike. It’s probably my favorite low-level PF RPG module so far, and what's even better is that it’s written for Kaer Maga. Buy the excellent ‘City of Strangers’ along with this adventure, and you have the all the material you need to start a killer campaign!