Heroes of Might and Magic III Complete is and will be one of my top 5 favorite PC games of all time. It's epic. It's timeless. Its music never gets old. It's like the best board game ever invented and put into computer game form. It has an awesome map editor.
I've been on a Heroes kick this past month, and as usual, D&D has been on my mind and has been looking for inspiration. Heroes of Might and Magic III has some great mechanics that could be inspiring for D&D ideas.