This is a comprehensive list of every faction, unit, and campaign pack ever sold for Rome II in order of release. We imagine that Rome 2 mods help with that, as does the DLC library.
It may not be the shiniest historical Total War game anymore, but Total War: Rome II still wants to be your friend. Even no, it still pulls in a respectable 5-6,000 players on average a day, and is only just behind the newer Three Kingdoms is at at the moment.