This was one of those bizarre adventures to me. It's getting lots of love in reviews, but I have to wonder how many of those are from people reading through it as opposed to actually running it, because it's a huge mess. Lots of great idea, but horrible execution on so many things. You CAN make it a great adventure, but it will require a lot of work rewriting what the designers wrote poorly.
My biggest complaint was Chapter 3. Although it starts out with a (literal) bang, the entire chapter is a bizarre railroad of doing things a specific, non-intuitive way. Partially my fault because I sped through Chapter 2 and started Chapter 3 before I was ready, but my group threw me for a loop when they immediately interrogated the witnesses to the explosion and wanted to track down the wounded man who fled the scene with the McGuffin. And then I realized that there's nothing in the adventure to address this incredibly obvious option nor trying to track down the construct. Instead, the only option presented (other than the far out there suggestion of breaking into the city morgue and casting Speak With Dead) is to try to track down where the construct might have been made, go through some so-so RP interaction with one of the priests, and then think to cast Detect Magic on the one item that will help them, find their way to the Manor (presuming you skipped a nonsensical RP encounter that is just an Easter Egg for the DM and probably dull and pointless to the PCs), and find out that there's two different groups of people fighting there, neither of which wants the PCs there nor will the PCs understand what is happening (with the adventure as written). And that's what happened: I basically kept skipping my PCs through parts that weren't making sense to them so they could find out the Nimblewright was at the manor, and they rushed in to defend the manor's guards against the Zhentarim assailants, only to be politely thanked and asked to leave once done.
Chapter 1 and 2 are a little thin, but I think it's not too hard to get a little creative and flesh them out. Chapter 4 is annoying in the railroading of the 8 Encounter Sequence that might as well be called "Sorry Team, but Your McGuffin is in another encounter", but you could probably smooth out the transitions as others have suggested while leaving the overall structure intact. Maybe change the encounters to either be tracking down additional clues and/or finding the 3 keys to open the vault as opposed to "JUST as you caught up with the Rogue who had the Stone, he throws a Hail Mary pass to another NPC who shows up and flees to another encounter". But Chapter 3 is the one I personally think needs the most DM work, to come up with a more viable path from Explosion to fight at the Gralhund Estate, preferably with one that utilizes more player agency.
Overall, if you want to retool the adventure, try to think up of ways where the PCs could logically use decision-making and skill to progress the plot. As written, IMO, too much of it was Do the Thing the designer intended/successfully make X check or else go back to the Tavern and cool your heels until an NPC helpfully comes along and tells them what to do. Because that's the Success/Failure state of so much of the adventure: Successfully do something the designer intended in Encounter A to figure out how to get to Encounter B, or an NPC will come along and tell you how to get to Encounter B.
