I looked at the twitter and found its a combination of hg and main but is there a more detailed description?
Welcome to McRPG
Welcome to MCRPG epicwin!
I would recommend reading this if you are new: http://www.mcrpg.com/minecraft-pvp/frequently-asked-questions/
OK, so its like the raid server in that it is constantly the same map, but with a lot of modifications?
Pretty close, yep.
That's the one!
Tracking is still the same, you can still raid bases and make your own awesome base too!
You just have more things in place to protect your base, and some cool things to help you while you play