I played this campaign...
And overall, I was somewhat disappointed with the game.
The player accumulates power, but then what?

1. Completing the game with one hero and one unit, until mana runs out.
2. Completing the game with one hero and a small number of units after 2 weeks, when the opponent has developed a bit, and one unit won't be enough to defeat them.
3. Completing the map with a powerful hero, sweeping away everything in their path.
4. Building magic towers to obtain the remaining high-level spells. It's tedious and takes a long time to accumulate resources for building the towers.

I think, since the series has deteriorated, modifications should be introduced. For example, at the beginning, give the hero not 0-0-0-0, but 0-0-5-5. Also, give larger and longer maps to make it more interesting to play.
Suggest what else can be done.