The style of the building is hard for me to pin down. It was designed around the time the famous Paris Exposition internationale des arts décoratifs et industriels modernes of 1925 was so recent that its "Art Deco" impact had yet to be strongly felt in America. On the other hand Urban, Austrian born, was highly aware of European design trends and seems to have incorporated some of the non-geometric Parisian Deco along with his own post- Art Nouveau design sympathies.
The resulting building and its interior décor was rather busy looking, certainly by orthodox Modernist standards of European architects of the time. For us, had it survived, the Ziegfeld Theatre would be a fascinating document of mid-1920s design by leaders in their fields.