This modding API is missing many, MANY features, that you may have used in the old R2API. The file loading of LanguageAPI has been stripped, because it never saw much use. This will break language mods, but it can always be added later. It's also missing DoTAPI, because very few mods used it and thus, didn't seem necessary for the first release.
EnigmaticThunder is a new modding framework for other mods to work in, its creation was fueled by the lack of a working standard API for mod developers to use. As such, it provides many features (most from the old R2API).
At its core, it should be an easy to use API that's easy to transition to from R2API. See the transitioning section for more details.
The contents of EnigmaticThunder should be extracted into the BepInEx folder, such that the files inside in plugins in the archive is inside your plugins folder.
Much of the documentation is in the included xmldocs, and further information may be on the dedicated the modding discord.
Since EnigmaticThunder provides many features that R2API had, it should be easy to transition from R2API. For example, the functionality BuffAPI offered is now provided in a class called Buffs, contained within the EnigmaticThunder.Modules namespace. The functionality that LoadoutAPI offered is now offered within the class Loadouts, contained within the same namespace. For skin mods and survivor mods alike, it should be simple to transition.
Unless you are a mod developer, this section will not be helpful. Unfortunately, there's no azure pipeline yet. You can get the mod from here and be able to build it without hassle.
0.1.1
0.1.0