Well, the gist of it is that Dark Moon is corporate dystopian, cyberpunk setting mainy taking place in Canterlot aprovimatly twenty years in the future the Open Equestria thread.
I'd recommend reading the lore doc for a more in depth rundown of the current world.
As for feel, It's almost near constant rain or drizzle, cops are bankrupt and a cybered up private police paid by the corps run the streets, justice usually goes to the highest bank account, 'Big brother' is almost always watching, mutants exist but are basically third class citizens or lower except for the very rare few.
The moods for scenes may vary greatly but the overall theme is intended to be quite oppressive and dismal to n extent.
I'd make a comparison to "Shadowrun" if your familiar with it.
Arcs however.... are mainly in the 'starting' phases at this point. Things that are important to arcs are commonly mentioned in the "Datapress Headlines" near the bottom of the OP's for the threads. Those are updated when the next thread is made.
>You didn't mention it, but combat is either d20 or honor system depending on the people involved. Thought I might mention it.