This is a great upgrade game for those mature EQ2/WoW players, IMO. I'm not a WoW player (I played DDO) so I am still on the fence as to whether or not I like it.
And, oddly enough, most of my characters are on the Omm server as well.
PvP on the PvP servers seems to be a Free-for-all from what I can tell, except for the safe zones. I am note sure where you can tell if a zone is safe, but I suspect the cities. I don't know since I have only been on Hyboria (PvP-RP) for a couple hours. Several people tried to gank me, but my assassin was able to escape them by Hiding. From what I hear the Hide skill is crucial for PvP servers.