This is what is adds:

-New focus trees, generals, companies, and ministers for Romania, Hungary, Czechoslovakia and Yugoslavia including
alternate history paths.

-New 3d models for vehicles, planes and infantry as well as accompanying 2d art for the new nations

-3 new war themed music tracks by composer Andreas Waldetoft

-Voice over sounds for infantry units in Czechoslovakia, Romania and Hungary

-You can now License Produce equipment from other nations

-Added Equipment conversion ability on production lines that allow you to convert older equipment to newer and/or self-
propelled models

-Added 2 new industry techs that allow you to improve conversion efficiency

-New subject levels for fascist nations: Satellite, Reichsprotectorate and Reichskommisariat

-Added 10 new achievements

All features should be in the base game and shouldnt be pay walled. Buy it but wait for sales.

One of the few hoi4 dlcs that are worth the money because you get:
- National focus trees for China, Communist China, Manchukuo and the Warlords
- Modified focus trees for Germany and Japan
- General traits and abilities
- Ability to send attachés
- Ability to send volunteer air corps
- Formable nations that can be formed through decisions
- Autonomy levels for subjects of Japan (and subjects of Manchukuo if it becomes independent)

nevertheless you should wait for sales