This module should be double sized. It's missing the map of Glimmerhold, but I found it online. The premise is sound, but the dungeon into Siege Weapon needs more 'crunch' dealing with hazards and CR rewards, a timeline as the rooms change, etc. I would have liked to see more detail of the Doom Guides as an organization, perhaps a charismatic leader with which to respond or interact with. These people are very interesting, since they clue the PCs into the corrupt nature of Glimmerhold. Also in the text, are suggestions for NPCs whom would interact with the PCs, but no names or even base stats are included. Again, this module shouts out for more detail.
A bit of background: I am running this adventure chopped up with the 'Doom Grinder' from TSR circa 1998 (?). I have set this module/Doom Grinder as the dwarf city of Karakast, on the fringes of the lands of Greyhawk. My Age of Worms campaign has a larger than normal group, so XP progression from that AP is slower than normal. The PC group is 6 level 12 characters. So I used the advanced template for most of the bad guys. Added some Forge Fiends rather than the Fire Elementals. etc.
The Doom Grinder module as written was interesting, but no reason for it's existence, reason for it's course, and the Derro guiding it was sketchy (i.e. they're insane, so do insane things). The 'Clash of Kingslayers' has motivation in spades, and I love the interaction with the King!