Right, the mages are amazing (at higher levels/research, and with the forge bonus)... Some devastating spells and very decent HP for a mage, so they don't die if you're not coddling them every second. But the standard units kind get knocked on a bit...
You've got the same problem with the Fire barracks units as the Chaos ones, in that they're all glass cannons that aren't the easiest to use unless you've got great numeric superiority and some decent micro skillz. This is probably because the barracks units are the exact same units, aside from the champion and ship (which Chaos actually trumps). I was always a bit saddened that Fire didn't get their own unique infantry unit... I like Fire.
As for ranged units, they're granted a thief champion who can hide about as well as a hippo with irritable bowel syndrome (apparently they're not half bad at shooting though, so there's that), and a ranged unit who's really quite impressively good... If he weren't single-unit instead of the three-unit deal every other faith gets, meaning that while he is very good on a unit-by-unit comparison... He has to carry the weight of three archers firing three projectiles. That changes things.
Their magic units, on the other hand... Well now we're talking. Expensive as balls, but Fire delivers. Elementals, demons, dragons and the legendary Fafnir all put down some very respectable smackdown.
Order is actually quite decent. They've got some brilliant support spells that help out their standard troops (heroic demise is *brutal* if used properly), and the standard troops are nothing to sneer at on their own. Order units have quite high armor, even at low levels, which means they can just shrug off a number of attacks and keep carrying on. Combined with decent attack values and okay movement speed, Order provides a rather solid attack force that lends itself wonderfully to longer war campaigns due to low attrition. Their cavalry units are just all-round superior to the infantry, and are the only basic troops in the game that can be upgraded to level 6 (via knighthood). Crossbowmen are okay, putting out some very painful damage, but they've only got moderate range and firing speed, so they're best just sitting back and supporting the frontliners while the wall of armor out there stops the horde.
Also, best capital resource enhancement spell. Inspiration increases ALL production by 1. However, I've never quite figured out the perfect way to give them a good jumpstart in the game...