I would not recommend this mod for the light hearted, especially at high tier.
Each encounter is tough with a high potential for character death. The optional encounter is particularly deadly and will almost certainly take out a PC at high tier.
That said, at the end of the mod, each PC will have earned their chronicle.
Breakdown of my experience with the module:
Played at tier 10-11.
Ninja 7/Shadow Dancer 3 w/Shadow Companion
Ranger 10 w/Wolf Companion
Fey Blooded Sorcerer 9 or 8 (I wasn't sure)
Diviner Wizard 11
With a high Diplomacy Paladin, the Ratfolk were easily talked into taking the party to meet the captain of the guard. The captain was also Diplomacied to allow passage through the Sundered Path.
This is where things got a little ridiculous. Deeper Darkness and Dispel Magic in unison hurt the whole party. With the addition of Sneak Attack, we were lucky to have a Paladin who was healing himself with Swift Actions and a caster with Daylight as a Preferred Spell.
A swarm in a fragile cavern. Luckily our Arcanist made the Knowledge check to determine that the cavern could cave in should there be any significant disturbance, like a fireball for example. We were able to get to safety and the Wizard brought down the roof, literally, with a Fireball.
Encounter 4 (Optional Encounter):
We had sent the Shadow Dancer's Shadow through the rockfall to determine how long it would take to clear. Reasoning it would take a considerable amount of time, we decided to rest. The Paladin took the majority of the watch after taking first rest (he had a Ring of Sustenance) but had not yet prayed to regain his spells when the party was ambushed by the two Advanced Gugs. The Paladin did not notice their approach so they were able to get their move in the Surprise Round. He then beat them on Initiative but was unable to kill one in a Full Attack action after Smiting. The party mostly awoke to the sounds of combat (this may have been due to an error by the GM, DC to hear battle is not 0, but -10 so when sleeping, the DC is 0, not 10). The gugs proceeded to act and one rounded the Paladin with Awesome Blow, AoO, AoO followed by a full attack from the other Gug. The Wizard then cast Glitterdust. The Sorcerer and the Wizard proceeded to create pits and then the Wizard D-Doored the Shadow Dancer, Ranger and Sorcerer to the other side of them. The Wolf was killed but the rest of the combat was spent whittling the Gugs down from the other side of the pits.
With the loss of the Paladin, the party decided to just offer tribute to the Dragon.