Ack, sorry! Life got very busy recently and I forgot to check back in on this thread! Let me see if I can think of some things:
Adventure 1: The last confrontation with the wounded Asrabey is very cool. My PCs didn't even think about trying to fight him, but if you have a trigger happy group, I'd suggest giving him a brooch of shielding so that they can't just automatically take him down with a magic missile. Make them earn that victory.
Adventure 2: MacBannin is pretty weak as statted up. My players took him down in one round. I'd suggest beefing up his HP or giving him some magical defenses.
Adventure 3: The rainbow room in the dungeon is very complicated. My players just avoided it completely and took a different route.
Adventure 4: Perfect, don't change a thing! Just be sure you understand the NPCs' motivations and personalities and play up that RP on the train.
Adventure 5: My players loved the crimebusting minigame and the scenes with the B-team. The party managed to track down and capture Lorcan Kell before he could murder the B-team members. The intercepted his carriage when he tried to flee to the Bleak Gate facility under Cauldron Hill. I replaced him in the factory battle with an undead version of the tiefling gunslinger Boone, whom one PC had murdered during the previous adventure. (I used the stats for a pale stranger.) I ended up just narrating the final ship battle against the colossus. My party didn't really enjoy the naval rules and fighting a few random oozes after the showdown in the factory seemed a bit anticlimactic.
Adventure 6: I felt the railroad challenge was a little more complicated than it needed to be, so I handwaved portions of it. The party bard managed to charm Terakalir in the final fight and rode her around to help take down Lya and her goons, so that was fun.
Adventure 7: Really fantastic. My party loved infiltrating the Ob in disguise and the tense roleplaying that resulted from it. One player perma-died though, which kind of sucked. PCs better be careful here!
Adventure 8: My players tracked down all of the memories and fully got Kasvarina on their side. I didn't use the "no rolls higher than 30" rules in Methia. The party ended up sneaking past all of the encounters to the tower. The fight at the end is epic and awesome. One minor complaint though is that as written, Kasvarina disappears after this adventure until the very end of the campaign. It seemed a shame to have her vanish after everything they went through together, so I had her stay with the party through the beginning of adventure 10, when she went off to aid the eladrin enclaves against the Ob (which lead to her capture).
Adventure 9: Lots of good stuff here. Make sure you understand all the different moving parts of the palace fight.
Adventure 10: Pretty straightforward adventure. Didn't change anything.
Adventure 11: My players were bummed that Vitus Sigismund took such a heel turn, but that's what happens when the world breaks. They enjoyed finally taking down Sijhen.
Adventure 12: Awesome, Planescape-style shenanigans. They lured the giant undead-hating sun all the way to the mouth of the Gyre to burn the Voice of Rot. I had to triple his HP just to give him a fighting chance against the PCs, but he still went down in three rounds. Low touch AC is a death sentence against spellcasters and gunslingers.
Adventure 13: Again, make sure you use the checklist in the final encounter. It is your friend! And be prepared for whatever ridiculous 20th-level tricks your PCs can do. They're basically unstoppable at this point, but make things seem like a challenge at least.
Most importantly, have fun!
