Spoiler
I figured I would put this all in one convenient location. Faction differences in gameplay, as stated by the official releases of each faction:
Rome - Rome benefits economically from its excellence in metalwork, enjoys enhanced military development, and can exploit the masses in order to maintain public order. Furthermore, the player will choose to conduct the affairs of Rome as the head of one of three great Roman houses: The Julia, The Cornelia, and the Junia, each of which brings further economic, military and cultural benefits. (Yes, you get to choose one of three leaders, that's awesome) Well-drilled, well-equipped heavy infantry form the backbone of the army.
Carthage - Carthage benefits from its mastery of the waves and its heritage as a great trading nation. As a democracy, it also enjoys an improved level of population happiness. The player also has the choice to play as one of three major political powers, each of which confers further military, economic and cultural benefits. The bulk of its armies consist of mercenary units.
Macedon - Macedon gains advantages when fighting other Hellenic factions, and enjoys improved income and provincial growth from every client state owned. Experienced warriors, the armies of Macedon also have an advantage when fighting against barbarians. Macedon also has a harder time forming diplomatic relations with other Hellenic States.
Iceni - Brave and warlike; invoking the goddess Andraste as they charge into battle drives them to even greater feats of valour. Their expertise with iron makes the resource a particularly effective form of income for the tribe, as does their skill at raiding and looting. And as a warrior society, the happiness of the people increases with every fresh declaration of war. The Iceni principally make use of infantry when at war. Equipped with large oval or sub-rectangular shields and either a sword or spear, their main distinction from the Celtic tribes of the continent is the practice of painting or tattooing their skin, combined with a greater use of slings in battle. Although light cavalry are used, the Iceni and other British tribes are famed for their highly manoeuvrable war-chariots. After harrying the enemy with javelins, warriors dismount and engage in a fashion similar to the Homeric champions.
Arveni (Gaul) - Noted craftsmen, the Arverni enjoy improved income from their artisans, as well as profiting from the Gauls’ expertise with gold-working. In battle, their cavalry benefit from natural Gallic horsemanship, while the charisma and fighting prowess of their kings and chieftains make them formidable warriors, and earns them diplomatic respect amongst other barbarian tribes. Heavily dependent on infantry, the Arverni make great use of javelins and the devastating impact of the charge, led by elite warriors such as Spear Nobles and Oathsworn.
Suebi - Masters of forest warfare and plunder, stemming from a confederation of smaller Germanic tribes. They have a diplomatic edge when dealing with other barbarians and excel at fighting lesser tribes who dare to stand in their way. They feel disdain for outsiders, civilised cultures and other barbarians alike, and must contend with considerable resistance from those whom they conquer. Heavily reliant on infantry and ambush tactics, raiding is their predominant form of conflict. Lightly equipped, most Suebi warriors make use of the framea, a javelin-like spear, as swords are a rarity. Often unarmoured they carried their rounded, oval or long, hexagonal shields into battle and wore little more than simple cloaks or other garments at times.
Parthia - As an Eastern faction, Parthia profits from the rich heritage established by the Persian Empire both in its capacity for trade and in its cultural strength. A degree of tolerance for foreign cultures further eases Parthian conquest of new lands, but their Zoroastrian practices mean an aversion to slavery, which is detrimental to both the economy and to public order. In battle, their great marksmanship and mastery of cavalry makes them a force to be reckoned with when fighting on open ground. A confederation of tribes, Parthia is famed for its horses, nomadic horse-archers and heavy cavalry, the latter developing distinctive bronze or iron scaled armour which covers both horse and rider. For its infantry it relies on ethnic Persian/Iranian hillmen, spear and skirmisher units and sometimes mercenaries, armed and drilled in the Seleucid fashion.
Egypt - They are skilled statesmen and academics, and their naval prowess is unquestioned. The intermingling of Greek and Egyptian fighting styles provides the Ptolemaic Pharaohs with a military that is both advanced and balanced, yet still honours the role of the champion commander. Making great use of spear and pike, their forces are further diversified with skilled swordsmen, scythed chariots, and more exotic units such as African war elephants. Egypt's position on the Mediterranean Sea also requires a substantial navy to protect its colonial and trade interests.
Pontus (Free DLC) - Pontus enjoys healthy diplomatic dialogue with Greek states and successor kingdoms, and is noted for its resolution in battle, particularly against barbarian forces. However, the forsaking of its Persian origins means that eastern cultural influences within its provinces yield diminished public order benefits. Its prized commodities, and the opportunism of its well-informed rulers, have enabled Pontus to remain one of the strongest Hellenistic states in existence. With connections throughout the ancient world, largely due to control of Black Sea trade and exports of timber, precious metals and valuable steel, Pontic agents are perfectly placed to gather information on their enemies abroad.
Athens (Pre-order) - As a city state, the capital city of Athenai enjoys great wealth, and its rich classical heritage makes it easier for their conquests to convert to the Athenian way of life. Its strong naval tradition gives its fleets the upper hand, with the downside being that her land units are less developed. Athens’ military focus has long been its navy. However, continuing the traditions of the classical era, its citizens are also expected to contribute both infantry and cavalry to its armies, although mercenary troops now supplement their numbers. With a strong backbone of spear-bearing Hoplite units supported by archers, a fully formed-up Athenian army makes for a formidable sight – and a tough nut to crack.
Epirus (Pre-order) - Epirus is a nation of great commanders and, as such, its generals and admirals enjoy a greater command aura in battle. As a nation centred more around village life than the city, Epirus also gains increased income from smaller settlements. However, their chequered past with the Greek states and colonies means they suffer major penalties to diplomatic relations with other Hellenic factions. With an economy focused on a diverse and scattered agricultural base, most of Epirus' trade is conducted via its fishing ports on the Adriatic Sea.
Sparta (Pre-order) - Trained to a level of martial prowess few others achieve, Spartan troops are excellent warriors, and, due to their oppression of the Helot people, they suffer less public discontent due to slavery than other factions. However, due to their Laconic austerity and focus on military training, Sparta benefits less from natural resources.
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