Age of Wonders 4

Are there any players who have already played it and formed their opinion about the game?
How similar is it to Heroes 3, and is it worth playing for fans of the Heroes of Might and Magic series?

I've played all the games in the series, including the fourth. There are certain similarities with the Heroes games, but it's hard to call them very similar. Moreover, even if you compare the series, the fourth AoW will be closer to the fourth Heroes game:
- Units in the game can move around the map without a hero in the squad, but they don't have the same range of actions.
- Heroes are needed to capture and create new cities, as well as to clear certain locations.
- Heroes are present in battle as separate combat units.
- Depending on their development, they can enhance the other units in the army.
- All hired heroes, except for those created by the player, have their own unique trait-specialization, which gives them a special active or passive ability.
- Both games are turn-based strategies in the fantasy genre.
- The use of magic is an important element of tactical battles.
- A number of other, superficial, similarities. For example, neutral units can, instead of fighting, offer to join in exchange for resources. Or the presence of a dungeon, as in the fourth game, where defeated heroes end up.

If you want something similar to Heroes, then this isn't quite the game I would recommend. Songs of Conquest or even Hero's Hour will be closer. AoW will be closer to Master of Magic than to HoMM. However, if you just want to play a quality fantasy strategy game, then I would advise you to give it a chance. In my opinion, it is one of the best games in the genre at the moment.