What is your opinion about Heroes IV?

But if you look at it from the perspective of a map creator, it's a complete disaster.
I haven't seen a more clunky map editor anywhere! In this regard, the fourth game is the worst!

O_O Em, have you even used the editor for the fourth game? Isn't it considered to be at least the easiest to learn and very functional? The only thing it lacks is more variety in landscape design, but otherwise, you can use it to realize even very bold ideas.

The same goes for the fourth game. There are more fans of the third game!

1) Fans of the third game are mostly conservatives.
2) The fourth game is a departure from the established foundations of the first three games.
So, neither the editors nor the plot have anything to do with the popularity or unpopularity of this installment in the series.

The Georgians wanted something too, but they ended up with a 58-year-old.

I don't understand what the example is supposed to mean. Do you think they should have created a new world-threatening evil (or better yet, tried to destroy Erathia again) and called on the old heroes for help? The entire "plot" of the third game is just pieces of Might and Magic; that's where the plot is, while the Campaigns in the third game are the most boring aspect of the game. Only the Chronicles are interesting, but only from a literary point of view.
As for the fourth game, this change in the world and the main characters, in my opinion, fits in quite harmoniously. The old heroes "had their fun" and ruined the world, but it wasn't quite the end, and as it is said in the opening cinematic of the fourth game, "we are turning the page again." And in terms of gameplay, this change is also quite normal. Since they went for global changes, they went all the way.
This is not like the fifth game, which was made from who knows what in terms of plot. That's where the mediocrity lies...