My personal take on the armies:
Firstborn: Looking for the best fighters in the game? Look no further. The Firstborn grunts are really, really good, and the Firstborn special units and characters are simply brutal.
Devout: Uninspiring grunts and hordes of skeletons augmented by demonic creatures of every shape and colour. This is the army you'll play when you're into big, hulking monstrosities...
Elves: Somewhat whimpy compared with the Firstborn, the Elves make up for that with mass, and more importantly with Magic. Summoned creatures and spell-augmented special units galore.
Swamp Goblins: These feral Goblins could never stand up to the other races in a fair fight. Trouble is: they ain't fighting fair. Guerilla tactics, poison and giant insect mounts combine to a surprisingly capable and powerful army.
Stygian: Ancient evil Lizards that run like the wind and hit like a hammer. Combined with their more than respectable magic capabilities, this is an army that can easily outmaneuver the enemy and pick it's own fights.
Sons of Kronos: Naked berserk barbarians. Don't let them get shot at by archers, for they'll die quick and unglorious. But get them into melee, and watch how they make mincemeat of just about any enemy in short order.
Dwarves: Walking tanks with giant walking demi-gods and a few nasty tricks up their sleeves. Slow, but damn are they hard to kill.
Blackbloods: The swiss army knife of Chronopia armies. Something of everything, not excelling at anything (except fast cavalry...), but they'll always have *something* to handle just about any situation that comes up on the battlefield.
Personally, I play everything safe the Devout (and that will also only be a matter of time...), and I must say that I'm having the best fun with my Blackblood, Swamp Goblin and Sons of Kronos armies. The Swampies definitively can do well without Jade House Elven allies, and are a fun army to play that's definitively doing some things differently...