Scale is smaller than that seen in the similar army-vs-army Total War games - but then again, what isn't? Units are commanded by regiment, not by individual, and generally you need to look after no more than five or six regiments per battle. They have been balanced along the usual rock-paper-scissors formula, so tactics are always vital.
The effects of map terrain also play a role, as every scenario features valleys, hills, forests, and even swamps that mess with unit effectiveness. Mashing armies together gets you killed in short order, so you need to learn when (and where) to wade into the action with melee marauders and when to sit back and let your axemen take care of things.
Much of the game revolves around heroes, though. They have a tremendous amount of RPG depth, including a full range of stats, equipment from magical armor to potions, and can even be used to square off with enemy heroes in duels.
Also, just like in the usual D&D -style fantasy role-playing games, heroes can be leveled up and can select from over a dozen skills spread out in combat, duel, and command schools of expertise. So if you want to be a better melee fighter, you might put points towards something like the magic-and-morale-boosting Screaming Death. To improve as a duelist, you would look into Deadly Strike, which increases damage. And to best command troops, you consider Inspired Leader to raise morale and attack percentages.