Combat units are fairly well-balanced, each with inherent strengths and weaknesses expressed through armor, mobility, organization, and morale ratings. Infantry units include Auxilia, Legions, Gladiators, Praetorians, and, lest we forget, the lowly peasant. Cavalry are mounted soldiers who can tear across a battlefield faster than anything else. Ballistic attacks may be launched by Archers and Velites, both of whom can also hold their own fairly well in close-quarters combat. All units accrue experience points during battle, making them fiercer fighters in subsequent battles, so it's a good idea not to use your veterans as fodder against a massively superior force -- know when to hold 'em, know when to fold 'em. By the way, all of the above units are unique to the Roman Empire; play as other factions, and you'll have different units available to you, though each will be roughly equivalent to its Roman counterpart.
A concerted effort has been made to make Legion's system requirements as reasonable as possible, which means first and foremost that there's no crazy Warcraft III-style modeling or detail. The main reason for that seems to be the sheer size of the forces involved in many battles; there may be literally hundreds of combatants on the screen at one time, making 3D units a practical impossibility even for a decently-equipped G4. It's the price one pays for epic scale. The depiction of buildings in the city management screen answers my perennial question regarding cities in similar games, namely, "where the hell do all these people live?" Here, scattered throughout cities, you'll see little groups of residential structures, which have no interactive purpose, but they do add a little bit of realism to the scene.
Legion's audio elements consist mostly of a pleasant, low-key soundtrack that runs throughout, and that turns appropriately martial when you enter a battle phase. Battle is where sound plays the biggest part. You'll hear it all: thundering hooves, clashing swords, screaming warriors. If the music or the sound effects aren't your bag, though, each can be turned down or off independently.
Legion will run on OS 9.2.x and OS 10.1.3 or later, with a G3 or G4 processor (Freeverse recommends an 800 Mhz G4, but I got by nicely with half that speed, and 800 MB of RAM).
So, those of you who like your battles epic, but are sticklers for historical accuracy, rejoice. Legion will soon be cutting a swath of destruction to a software store near you. Ave Caesar!