I finished it. I had to learn the console commands. After the second mission, the rest are a piece of cake. Well, Ossir annoyed me by being able to swim without penalties for landing/unloading. Only hitting him with area-of-effect Chaos magic helped so he wouldn't have time to escape. With the Angels/Vampires, I didn't understand at what stage the choice was supposed to be made. It seemed like I needed to go to the sacrificial altar, but it never became available, and I was able to build the Angels (which is generally good - I don't think Marcel needs troops at all, except for ghosts), but why? In the third mission, it's nice to explore, scout everything, and the presence of quest fairies is also cool. The elf didn't impress me (not at all), and she was also defeated without additional troops, it seems. The fourth mission - everything is also defeated like a walk in the park as you progress. I didn't understand with Godric; he was supposed to have a treaty, and he wasn't supposed to attack, but he immediately showed up in the dungeon and died first. With the Treasury, something happened - Iranna escaped, she wasn't bought back, and I couldn't take the book. Well, I like to be resourceful - I lured her out, set up empty heroes, retreated, waited a couple of weeks, and the result was amusing - the Castle was reduced to zero (and that's with the fact that there is one Necropolis, and there you can quite easily kill troops to the desired level). And it's not that close to the exit either. I didn't give it back. The only serious battle was with Miv - I attacked her with pink ghosts, and there were about 300 knights of two types, and the rest were also in good order. If there is an opportunity not to hide, then why not use it. The inscription on the quest tomb was very amusing, and the texts are excellent in general. Conclusion - I repeat, the campaign is raw, but it has potential; it would be nice to refine it...

Added 12 minutes ago

I mean, we need to plan our build, and for that, we need the console...

Thank you, as I usually don't use the console, it didn't occur to me, but it's a perfectly viable option. I only remember the console when there's a scenario snag, like here in the second mission.

Added 3 minutes ago

the only thing I don't understand is whether Berserker and Subdue are blocked at all levels, or I'm just lucky

Subdue is blocked (the Tome of Darkness is the indicator), and with Berserker, it's just "you're lucky."