Yep, that's the gist. I remember it fondly from the xbox era, the only game I miss from that console actually. It's a clusterfuck, but if it clicks for you, it provides a form of gameplay I've never experienced. It's divided in a serie of different campaigns, one per general. You have both field battles and strategic movement on a map which is more or less linear, little detours here and there and a few optional battles. In cities and encampments you can equip and level up your troops, liutenants and General, there's a basic skill trees which determines which kind of units your officers can command.
In Musou mode, you control your uber general and generate SP by performing moves and hitting enemies. You can control and give orders to your various regiments, although you rarely have more than 2-3 at a time and iirc never more than 4. Your general is always accompanied by a melee unit of his own.
Regiments can generate SP themselves by performing special actions. Charging cavalry is the best SP engine and mounted archers are a pita to setup properly but can also inflict good damage on top of SP generation from simple reanged attacks, like archers. Lancers/axe throwers stop charges and collect SP that way.
You can use said SP to power spells from your general or liutenant (one per regiment plus 2 accompanying your general in his own unit) or for special abilities, like Scorpion's earthquake. Spells are pretty basic, nukes and healing mostly but they do offer an added layer and are generally fun to use. Some units, like the swamp mammoth, are ginormous in size and impressive for the game era.
In this one you have an human army and Dark elves + orcs, the second chapter expands on factions, separating Elves and Orcs better (although some campaigns offer the old mixed army setup) and adding nice units like elementals.
