I think I will just talk about various different factions.
I find that playing as catholic nations can add a new depth to both the religious and political side of them game do to how the pope works and the crusades.
Playing as a Muslim faction means that you aren't on any sort of leash and jihads can be a great invasion tool and a way to unite yourself with the other Muslim factions
As an orthodox nation you are on your own.
Another factor I think would be land or sea. As a land nation such as HRE or France you usually start with a large amount of land and it can be really fun because will likely have to fight many wars on different fronts. Some land factions start up weak and have to take over land and establish themselves, such as Russia, Poland, and Hungary.
As a seafaring nation such as Venice, Milan, Sicily, and Denmark you will have to colonize and trade. It can be a nice challenge attempting to control the seas and setting up good trade.
Then their are nations that are sort of a hybrid between the 2, such as the byzantine Empire, England, and the Muslim factions.
I feel like total war has declined, the first 2 games were good for their time but in my opinion Medieval 2 and Rome 1 are total wars prime and golden age.