I finally got around to playing this custom campaign. What can I say about it overall?
Story: I would call this prequel to the original campaign quite good and well-made. The story is simple, but no less interesting because of it. Knowing what will happen in the end, it's still interesting to see how the author envisioned this situation in the final cutscene.
Gameplay: There are some drawbacks here, especially in maps 3 and 4, where the AI simply sits idle for the entire game on a large map, and you just wander around and level up. There are also no additional interesting quests, but that's the only negative thing I can say, and even that's a bit of a stretch. Most of the scripts and tasks are more or less taken from the original campaigns – this is evident, but I repeat – the impressions are positive; maybe some people will even like this kind of gameplay. As a creator, I understand how difficult it is to make a map interesting and not too easy.
In conclusion, I can assure you that this creation is definitely worth your attention. If I were asked to express myself in one phrase, it would be: "simple but tasteful" – that's the phrase.