Diablo 3 was far from a failure as it broke a number of financial records; the main problem was the game-design pitfall of basing a loot-based game around the Real Money Auction House. (which they fixed in the expansion)
In a way the Diablo 3 RMAH helped validate the modern freemium/gacha business model for mobile platforms.
In a way the Diablo 3 RMAH helped validate the modern freemium/gacha business model for mobile platforms.