I decided to try playing the city state mode, and choose greece and sparta, because greek cities was one of the factions I hadn't played as yet. My rules are: 1. abandon all cities but sparta in max 5 turns (it only took 3 turns), and 2. no expansion allowed except taking cities and giving them away in max 2 turns after capture. 3. don't build any better walls than level 1 around sparta. 4. punish all who start wars against you. Either force them to accept protectorate after a serious bashing, or destroy them completely.

So far I'm doing good, I got Carthage as a protectorate after decimating a force they sent to besiege Syracuse during the early turns when I was still in the process of abandoning the settlements. I thought the city state mode would be really hard, but actually it hasn't been yet, even though I've played nearly a game decade. I'm thinking about changing the rules and randomly choose five settlements on the map that I'm supposed to hold as colonies.

But when Carthage nearly got kicked out of Syracuse by the Scipii, I got an even better idea. After sending help to push the Scipii back, I decided that my new rule would be to help all factions who are attacked, by conquering and many of the cities of the attacking faction and giving the settlements, and perhaps also some monetary support, to the victims. My first target will be the Romans, who early showed their lack of honor by attacking both the mighty Spartans while they were still in the process of abandoning their unneeded settlements, and the honorable Carthaginians who stand by their side... Of course, the rules also say that if Carthage should attack any innocent faction, I'll have to stop protecting them and thereby lose my steady tribute income of over 5k denarii per turn...

Perhaps I should combine this new rule with the colonization system. I should try to take control over all rebel cities with greek starting culture and make them spartan colonies, as well as choosing 3-5 random settlements.

It's sad that you actually need as many rules as these to make the game challenging, but with these rules it might actually turn out to be fun. Also it might be the only way to make the game last long enough to see the AI field some of the better parts of their unit roosters...