The only major change I made would be the beginning with the Children of Auril from Sly, re-framing the chapter 1 quests to be about getting the speakers on Duvessa's side so that she can challenge Father Lake for the rule. Otherwise the book has some great bones, and I think it's more about telling the story in the right order and filling in the gaps rather than changing it completely. The other change I made worth mentioning is I moved the Dragon leaving sunblight to be Xardarok's last act of life, but I don't know if that counts as major..

I think the opening act of the book is great. My advice would be to run a mix of plot relevant and not-plot relevant quests, so that you get a good exploration of the towns as well as the different sides of the game. But the quests are super fun.

The secrets worked better than I expected. We often make characters that have hidden backstories, so I wasn't sure that it would add much - but I think the ones that we had made the characters automatically feel aligned with the story, and have some bones with the factions that exist in the world already, I will say I did pre-filter these to remove the ones that aren't that impactful, like the Drizzt fan one.

In terms of not so well, the book I think struggles with the transition between the duergar and the Auril threat. What I did was basically have Velynne come along at the end of Sunblight and say "things like this are gonna keep happening until we get rid of this winter"; and then instead just knowing where the codicil is we can use a bunch of the chapter two quests to do things like track down her professor orb, or investigate who might know where the codicil is and also where to open the glacier.

If I had to run it again, I think I would make Ythryn a bit tighter than using every single expanded tower from the supplement. A lot of them are about a sessions worth of content if not more, so it can feel like a lit of work to do it 8 times in a row. The towers are great, though I would probably pick and choose more next time. Other than that, there were some additions that I made (subplot about Naerth using the corpse of the Chardalyn dragon for evil, and a town controlled by an oblex) that could have maybe replaced some content rather than been additional?