Confusing in later levels...
In the later levels I couldn't really figure out how to keep from being overrun considering I was replenishing the battlefield with the leading units as fast as they died, but then eventually ran out of money to even summon the smaller guys because once I summoned these people they didn't kill enough orcs (or anyone, sometimes) before dying again.
I don't know if the fighting is random or deterministic, but if it is completely random, it needs to be a little less random. Being able to summon more people hinges totally on your comp a.i. guys being able to kill sufficient enemies. You can't control them, so they've got to be able to do it on their own. And I don't think they do.
Other than that, pretty fun after the first couple levels and I realized there actually is a small amount of strategy in it (picking who to summon on limited resources). It'd be nice if you could do something as a hero to push back the enemies you can't control though, periodically, like spells or something, and maybe more variety of bad guys for you to fight (that actually fight back, maybe?)