I really like the idea too!
If I remember correctly, Player controls a group of heroes with minions and can upgrade both heroes and cities in order to conquer all game world. It's all turn based, right ?
I have found this good explanation of gameplay: https://en.wikipedia.org/wiki/Heroes_of_Might_and_Magic#Gameplay
There is also another series of games set in that universe which begined everything and they are:
Might and Magic: The Secret of the Inner Sanctum
Might and Magic II: Gates to Another World
Might and Magic III: Isles of Terra
Might and Magic IV: Clouds of Xeen
Might and Magic V: Darkside of Xeen
Might and Magic: World of Xeen
Might and Magic VI: The Mandate of Heaven
Might and Magic VII: For Blood and Honor
Might and Magic VIII: Day of the Destroyer
Might and Magic IX
Might and Magic X: Legacy
(not made by original company)
You basically play as a group of adventures who do quests, kill monsters and other RPG stuff.
But in there you don't have castles and it's turn based only in combat.
There was also MUCH more epic plot than in heroes of might and magic.
The story in I-V is basically about trying to stop the rampage of Sheltem who turns out to be an android created by the Ancients (a technologically advanced race). He escapes at the endgames but is finally destroyed in world of Xeen.