- What are the drawbacks of Heroes 3? (What didn't you like about it?)

Regarding castles, I think the following: All structures, dwellings, fields, etc., are implied to be within the castle itself (around it, but supposedly behind the walls). So, there can also be oases in the lava (for comparison, consider the Hanging Gardens of Babylon – and around them is a desert).
In Heroes of Might and Magic V, it's a little better, but you can build any castle on a lawn (a flaw with the Dark Elves or Inferno). I think this is incurable...