Look here for an up-to-date list of features currently supported. Not every possible feature is implemented, but the server will update itself as new features come.
Dub and a D compiler (DMD, LDC or GDC) should be installed for the extension to work properly. This extension also doesn't work on its own, it provides functionality but no UI. Extensions from atom-ide-community (or the original atom-ide-ui package), and build should be installed.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.