We've advanced too far into the Early Modern Era for CK2 to be a good choice of game to make up a Rhoman government in.You guys play ck2 and eu4 right? Whats the best description for Rome's government in your opinion? I'd say its Imperial Absolute Autocracy but that's not totally true isn't it?
EU4 is set right in that time period so I'll have a go.
It's of course a monarchy but the real question is what the reforms they took on their chosen tier are. Though the next DLC is going to introduce a bunch more so maybe this is a question to come back to later.
Tier 1 Power Structure:
Autocracy. Not even a contest.
Tier 2 Noble Privileges:
Curtail Noble Privileges. Again not even a contest. Especially since it gives more tax.
Tier 3 Bureaucracy:
Centralized Bureaucracy. If there's anything the Rhomans are good at its making sure their territory is governed effectively to the betterment of the state.
Tier 4 The Administrative Cadre:
Meritocratic Recruitment. I also considered "Nobles of the Robe" which is nobility that starts to serve in administrative positions but I think meritocratic is more accurate,
Tier 5 Deliberative Assembly:
Royal Decree. I could also see "General Estates" but I think royal decree is a bit more fitting for where Rhomania is as of 1635.
Tier 6 Absolutism & Constitutionalism:
L’etat c’est moi. This one is more of a mechanics choice. The idea is 'less minimum autonomy in your provinces or more provinces can be zero?' It's really just 'are you playing wide or tall?' and the Rhomans almost certainly are playing tall. They have two large vassal states in Egypt and Sicily and a smaller one in Carthage and with the Anizzah (if they even count as vassals). Eastern territory doesn't count for these purposes since ingame they would use trade company mechanics.
Tier 7 Separation of Power:
Political Absolutism. The only other option involves a bicameral legislature and that's pretty un-Rhoman.