I have some inspired ideas on how to design a Diablo board game. In fact, I have contacted FFG on this; their reply was that they no longer have Blizzard's licensing rights to make their games. The following are my ideas. If you have any of your own ideas or even criticisms, feel free to fire them my way.
Let's talk about the components. First there must be a world map, then exploratory dungeon tiles. The dungeon maps must be made of diamond-shaped hexes. Every player chooses their hero character, and they each receive a Character Sheet, like StarCraft the Board Game. On the Sheet there is a Life globe depicted and a Resource globe depicted, depending on what character you are. In addition, there are stats on the Sheets, and a Character and Inventory Window, where we will be able to equip our hero.
The enemy will be controlled by an A.I. system, like Gears of War, although significantly much more different. The loot dropped by monsters scale with difficulty, depending on factors like the number of heroes, and the Act, level and stage.
In addition there is a Skill Deck and Skill Tree Sheet, to keep track of your experience level. To get new Skills, you will have to spend your experience points gained from killing spawns. There is a level track along the side of the world map, to record the levels of the characters.
There is a reference sheet for enemy spawns, listing their statistics and how they scale with the number of players, thus influencing the difficulty of the game.
That's all I will reveal now. I have yet to reveal the battle mechanic!
About loot, at the back of the enemy's wound token is a number with a plus sign, which determines the number you must roll on a D6, to get a loot.