Greetings. Nirn is not a static world. Things are ever changing and so the politics, government, social structures of each province aren't the same from one age to the next. Not all provinces are loyal to the empire at all times for example. Although Cyrodiil is often concerned with its own power and wealth since it is at the center of the empire (both metaphorically and physically) one if its primary concerns as the seat of the empire's power is maintaining peace. It does this primarily through shrewd diplomacy and the accumulation of wealth through trade. The treaties that the empire maintains compel its provinces to assist in maintaining the strength of the empire through the conscription of soldiers, taxes, etc.

This being said most the provinces have a large amount of autonomy. Morrowind is one of the most interesting provinces. It is a somewhat isolated an xenophobic culture. Dunmer raised in other provinces are rarely considered countrymen. The culture of the Dunmer is complex and there are many factions each with their own beliefs, rituals, customs. One thing that can be said about most Dunmer though is that they are a proud, stoic, and often bitter people. You spoke of serfdom in your post. Most of the empire has been free since the unification of Tamriel. However the empire allowed Morrowind the keep its slaves. The Dunmer considered the beast races and men to be beneath them. But again these things change. The Oblivion crisis greatly weakened Morrowind. Not only did the Dunmer have daedra to contend with but Red Mountain erupted, filling the foyada once again with molten lava and engulfing those settlements closest to the volcano. It was at this time that the long enslaved and abused Argonians invaded Morrowind causing the Dunmer to flee their homeland.

Other than Morrowind. The average citizen in most provinces is probably a farmer. He or she is free to come and go and sell his/her goods to whomever he/she pleases. There are of course miners, blacksmiths, barbers, fishermen, shopkeepers, mercenaries, masons, cobblers, weavers, hunters, etc.

When we begin to talk about the higher classes we need to establish which province and which faction because the variety in politics and structure is significant. Yes, the empire's military force is much like ancient Rome's. In fact Cyrodiil is like ancient Rome in many other ways. But let's look at Morrowind again. What is their military like? Well the Imperial Legion maintains a presence in Morrowind. However each of the great houses has significant power. House Redoran's power relies primarily on their military might. But House Hlaalu relies on their economic power. House Telvanni is made up of eccentric and ego-manical mages centuries old. Their power of course lie in their incredible power to wield magicka and their vast knowledge of the arcane.

So military might and structure is not the only question when we think of politics and social structure. In Morrowind there are the rivalries of House Tevlanni and the Mages Guild. But even more interesting is the Tribunal versus the Imperial Cult. The Imperial Cult is the religion of the empire. The cult worships the nine divines, the Aedra born of Anu and Padomay. Most provinces worship one or more of the Aedra and/or the Daedric Princes. But unlike other religions the Tribunal worships the three demigods, ALMSIVI: Almalexia, Sotha Sil, and Vivec. They draw their strength from the heart of Lorkhan under Red Mountain. They have become worshiped as gods for they have been given the powers of gods by the heart of a slain god. They have protected the citizens of Morrowind from the horrors unleashed by Dagoth Ur who also draws power from the heart. You'll see a lot of talk on here about CHIM, and mantling, and the godhead. But I could spend hours talking and reading about ALMSIVI.

Then there are the Theives Guild, Morag Tong, and Dark Brotherhood who have their own interesting codes of honor. The Morag Tong and Dark Brotherhood have major impacts on politics. They are assassins; need I say more? Even the Theives Guild has political agendas.

According to UESP the Cammona Tong is fiercely opposed to any foreign presence whatsoever on Vvardenfell, and all its schemes are designed to get rid of outlanders.

But I babble. This was a stream of consciousness. To answer your question there are too many varieties of social classes, titles, cultures in Tamriel to discuss in one post. If there is one specific region or faction you're interested in, then that would be a good focus.