What are the new occupations like? Does the Primitive Occupation give you two feats, or the choice between two feats?
Are the AdCs balanced with the AdCs in D20 Modern, or do they more resemble D20 Future AdCs instead? Are there any non-FX AdCs, and if so, how many? Can you use Archaic Weapons Proficiency as a pre-requisite for the Soldier?
What are the new feats like? Is Sidekick balanced? How does Obscure Knowledge work?
Why do the authors insist on "naming" firearms instead of just giving generic rules? There wouldn't be complaints about the M1 Garand if they avoided naming the guns. (Ok, that's not really something you can get from D20 Past.)
There's a lot of Nazi stat-blocks in the book. If you remove the allegiances to evil and Naziism, could they make interesting villains for other settings?