This post contains spoilers for the adventure. If you've not played it and think you might end up playing it some day, don't ready any further. This is especially true if you play D&D with me because I really want to run this.
I prefer the layout and style of the new version better. I didn't care for the layout or artwork in the original. It worked. The adventure was great, but it wasn't my cup of tea. The new artwork is unnerving and outstanding. Jez Gordon did 21 of the illustrations, the layout, and cartography. Here are a few examples:
As for the adventure itself, it feels much more cohesive than the original to me. The original adventure contained many weird scenes and encounters. They were all loosely tied together as being connected by a death cult. This connection is much more cohesive in Zak's version. The Duvan'Ku feel more whole than they did in the original. They are presented in all their unholy, horrific glory. Zak has included many notes about the original, how he presented the scenes in his game, and other options. I thought this was a really cool thing. The inclusion of music suggestions for different scenes is a welcome addition. I really look forward to running players through the Tombs of the Greater Repugnances. Each of these undead monstrosities is quite unique.
There are a few options included in the Hell Vomits Its Filth section. We are given exact numbers, stats, and different options for the hordes to look like.
It will probably be a while before I get to run this. I'm still in the early stages of my Forgotten Realms game. Once it's over I will run this as part of the Greyhawk game I mentioned.