I saw my first demon army today, six hundred and more goons. Scary sight on the map. The friendly armies of the campaign force I was in wouldn't go for it, but I managed to get them close enough when I attacked it that the numbers were within about a hundred or so.
It. Was. Awesome.
I tend to focus more on the killing than the numbers when a fight starts, but I definitely did run into the demons a couple of times, first time was at the start of the battle leading the initial cavalry charge, as I pick a bad guy, drop the lance and aim to spear him good. On this occasion I heard the stab, but no scream, looked down, the display said I'd hit something for over two hundred damage with a couched hit, but no XP was forthcoming, and that was when I knew I'd found one of the big guys. Of course by this point I was hurtling into the swarm of enemy infantry and I never saw the demon again, but had to have been one.
I'm on day ninety of the campaign, so I can't say I know how the demons and stuff pan out in the game, but here's a couple of things I would suggest that I think would improve them a little bit.
1. The giant army looks cool, but I don't think it's in keeping with the style of the game. The regular nations send out groups of armies, to handle things like scouting and foraging (okay that seems to only apply when I'm with them, but still it seems to be how they roll). One colossal army means that it's slow, it's rare that armies will engage with it and if they do it will just gobble them up. Now fair play, this is very cool to see, but I think if the heretic hordes consisted of multiple army groups, much as the lords do, they would be better.
2. The horde of cultists is one of the best armies I've fought against in the game so far. However I think the presence of too many spectacularly tough troops on a per army level kind of detracts from it. What I would suggest, bearing in mind what I said above, is divide the normal number of demons and other top troops they have in these armies between say six armies in a battle group, and then load these armies with maybe two or three hundred cultist types. Proper starry eyed converts. This makes these armies tough, but not incredibly tough, and provides great fights.
Okay so that's only two things. Thing is I guess you probably can't make armies of NPCs wandering around behave in the same way as a Lords army, so maybe having a big old campaign group thing won't work. But that said I wonder how viable it might be to make a nation of the heretics, have them hate everybody, not open to negotiation and basically just nom-nomming their way around the map.