All base game release maps (DFW Campaign maps, the JP-JW:Fk Chaos Theory maps, and the four Challenge mode maps after “Canada”) and Challenge mode skins and patterns are the only things locked when you first start playing JWE2. Everything else, including all DLC content, is unlocked from the start as of a major update this past Spring, except for the second Biosyn level if I can remember correctly.
The DFW Campaign maps are unlocked when you complete them. Chaos Theory maps are unlocked when you complete the JPIII and JW:FK games, and when you 3-star the others. The Challenge mode maps are unlocked when you 3-star them as well, but they can be played on said mode when you get enough stars on the others. Finally, the Challenge mode skin and pattern rewards are unlocked when you complete a respective map on any of the four difficulties you choose. There are two patterns and skins per Challenge maps: Canada, Germany, United Kingdom, Northwest USA, and Southwest USA. With two of the rewards being unlocked on "Medium" and “Hard” mode at minimum per said map.
Campaign mode has levels for the DFW Campaign that are locked but can be unlocked when you first start them.
