Is it going downhill?
Not recently, the new developers have been grinding.
Does it still get constant support?
As said above, recently there has been constant support and hot-fixes and whatnot.
Is the game balanced?
Yeah, or at least I like to think so.
Is there PvP? (heavy emphasis if yes?)
Nooooooooooooooooooooooooooooooooooooooooooo.
Is there a good community?
If you are cancerous and into memes then yeah, check out the official Reddit; /r/RotMG/.