How would you classify the architectural style of each world?

You can access some of the shells for each world in the debug menu to kind of give you an idea of what to do. It helps with making the world look more cohesive.
Willow Creek and Newcrest seem pretty neutral in style to me. I think just about any architectural style looks good there. In my save, I have an Edwardian-inspired look to it.
Oasis Springs-Mediterranean?
Windenburg-Tudor/Tudor-revival
Brindleton Bay- Dutch Colonial or Cape Cod
Forgotten Hollow-Gothic Revival?
Del Sol Valley-Mid-century modern but Georgian looks good in the Pinacles.
Those are the one off the top of my head. If you want, you can check out my save file thread, I have pics of what I've done with all the worlds up to Mt. Komorebi.

Willow Creek- Gingerbread Americanized Victorian
Oasis Springs- Modern mixed with Sowthwestern adobe style
Windenburg Stylized Tudor/European (I saw a lot of homes and businesses in this style when I lived in Germany years ago)
Brindelton Bay- Cape Cod Colonial
Forgotten Hollow- Gothic Victorian
Del Sol Valley- Mid Century/Ultra Modern
Glimmerbrook- Old School country cottage
Mt. Komorebi- Asian influenced Ultra Modern
Newcrest- There are no homes here but the scenery gives me an industrial modern feel. I sort of see renovated brick storefronts turned into modern homes here.