MDG is a marvelous way to configure Sparx Systems Enterprise Architect. It allows you to extend the standard UML dialect with domain specific elements. There are a couple of advantages with this. Firstly your models become clearer as the model elements are more easily to recognize as to what domain element is actually meant. Second you dont have to construct domain elements manually each time you need them but you just drag'n'drop them from a toolbox. Third by also limiting the number of elements the involved modellers do not need to know the whole UML language but only the relevant subset. Designing a custom EA environment is actually no wizzardry. However, there are some steps you should follow which do not appear to be obvious.
The currently published version contains a walk through the most important parts of MDG and so one could say it is complete as it is. However, there are a couple of areas I will elaborate in more detail in the next future. If you think that certain parts should be extended or if you miss something, please let me know.