I completed both missions. The first was "Heart of Chaos," and I didn't even look at the description. I really enjoyed it. "Heart of Chaos" is a simple but interesting campaign, with interactive elements and enjoyable heroes. I especially liked that in some cases, you can just crush everyone, like with the Archdemon. Chaos is a very strong character, and his special ability works great, but in my game, the cave beast didn't summon; instead, a fireball appeared out of nowhere. With other spells, there wasn't even an animation – just a portion of the troops disappeared. But that's not important. I enjoyed the mission, except for the final boss, of course. It's... well, there's no polite way to describe it. He has max luck and morale, while I have -10 and -10. He constantly gets buffs, while all my troops get debuffs. He can also cast spells manually, and he has an incredibly large army, plus they teleport in, and reinforcements arrive from nowhere. I suffered a lot with him; he's not a boss, but a machine for humiliating the player. But overall, the mission is very enjoyable.
I liked "Fallen Knight" even more, although it has more drawbacks. I played as the overpowered Dominick because Haffad is some kind of natural anomaly that casts a rather weak plague spell and not even on everyone. Dominick, on the other hand, crushes everything, especially with skeleton archers and imperial workers who shoot twice in a row... and with the Soldier's Luck skill, you can immediately deploy TWO squads from the stronghold. Haffad also has -10 morale, although by the middle of the game, people quickly turn into undead. The mission is quite hardcore, especially if you mess up like I did – I first captured the central castle and then ran to finish off the last one on the right. There was so much pressure that I had to replay. I don't understand why there were so many complaints about Alaric and that old woman. The old woman didn't revive after her death and the destruction of the castle, and I just locked up Alaric, giving one of the heroes I bought from the enemy 17 levels and all the unnecessary melee units (reapers, dragons, zombies). Alaric eventually tried to attack my hero after a couple of months of wandering back and forth, failed miserably, and after that, he didn't even leave the castle. That made me laugh. Overall, the map is amazing, with many multi-stage interactive elements that are not useless. The two-stage siege at the end is particularly great, although I didn't enjoy playing as that pathetic Haffad. I'm very disappointed with how Chaos was handled; I didn't even understand what his role was in the plot if he just died in the middle of the map? There was even a cutscene from the end of his mission, where the Holy Word suddenly appeared from nowhere... but Chaos died, or what happened? And what kind of monster was he, anyway? It seems they won't reveal the secret, now that Chaos is dead.
Overall, the map is quite easy, except for the battle with the library guardian, but there, the overpowered Sandro's cloak + berserk + subjugation does the trick... and the castle with mages, but subjugation solves that too... and the gnome castle as well....
Yes, in general, I don't think it's possible to complete without Darkness, especially if you destroy the undead cities, as I did – otherwise, there simply aren't enough troops for all the battles. I suffered the most with Chaos and the library guardian. Chaos is just insane; he reminded me of how the final boss of his scenario humiliated me. But berserk and smart subjugation saved the day. In the battle with the guardian, I just put only dragons in the corner, and I cast subjugation and berserk on the undead. That's how I won. The gnomes were a joke; the Arcat dragons never left the stronghold, even though I couldn't remove their evasion.
I also liked the final twist. I thought until the very end that Haffad would defeat Dominick and send him to die, but it turned out to be something else. (Yes, the ghost of Dominick didn't prove anything to me; I, drooling, thought it was some other Dominick).
What I didn't like was the mandatory battle with Haffad in some battles – I don't understand why; this pathetic invalid sat in the Sanctuary for the entire mission at level 1. Also, when loading a save, you often can't talk to NPCs, especially the bandit leader at the very beginning – I couldn't even activate the secondary quest the second time and later. I also liked the units on their buildings; archers on the towers are exactly what Heroes 5 was missing to be perfect. Haffad's Avatar of Death is also pretty cool. Overall, I really enjoyed this mission, even more than "Heart of Chaos"; I spent a long time reading the descriptions and looking at the unit models. I really liked the redesign of most of the human units into the new green archetype, as well as the redesign of the old units – the skeletons with double shot, for example.
Added 7 minutes ago
https://imgur.com/a/8949mwM
I forgot to attach the screenshots. As such, only Chaos poses a real danger; well, it's really terrible. Gate after gate after gate after gate, and on top of that, summoning demons from nowhere.
And the final battle, although there, the avatar easily solves the problem... https://imgur.com/a/5ybwMeb oh yes...
In short, I liked the battles much more than in "Heart of Chaos." If in "Heart of Chaos" you just need a lot of meat, then here you at least have to think with your head about what and how.