I've been reading through the first part of the adventure and I like it a lot.
However, when reading through the player's guide, I feel that the rule additions don't match with the core rules.
The theme feats often refer to once per combat. As far as I know, there are no abilities in the core rule set that function like that. I don't even think once per combat is a defined frequency in pathfinder and I have been unable to find it's definition in the player's guide.
The Docker’s Jank theme feat seems very similar to Swift Aid (a Combat feat) though it includes the character itself (ihmo, this is not the idea of the aid an other action) and is restricted to 4 other characters (and to once per combat).
As far as I know, the rangers Hunter's Bond is the only ability that is restricted to 'your companions' though it does not have a maximum number of characters it can affect. The Docker’s Jank theme feat seems to screw over parties larger than 5 people.
Icy End of the Earth Theme Feat speaks about stabilising a dead character. Exactly what is meant by this? The closest thing I'm aware of that has functionality somewhat similar to the feat is Breath of Life (a 5th level cleric spell which btw probably makes the feat severely overpowered). Though the amount of healing is specifically mentioned in the spell description.
Icy End of the Earth Theme Feat indicated the possibility to be stable at -100 hit points. I don't think the core rules cover this.
The Man with Two Guns is God: It offers quick draw and two weapon fighting with guns. Though it does not offer proficiency with guns. So your druid can quick draw guns and fire 2 weapons though can only shoot in his own foot because of the lack of proficiency?
All in all, I think ZEITGEIST has a lot of potential though it doesn't show easily.
Back to reading the campaign guide.