2. The Auction House - Diablo III
As hype as Diablo fans were for the series' first game in over a decade, Diablo III was released in 2012 to immediate controversy when, in addition to the presence of always-online DRM, the game's Auction House allowed players to purchase loot with real money.
Though initially conceived as an attempt to reduce risky third-party buying and selling of in-game items, allowing trading with physical cash cheapened the overall experience for many players, who felt that allowing people to pay their way to a sweet loadout was dangerously close to pay-to-win territory.
For the core contingent of Diablo fans, the thrill of these games has always been the glee of finding rare loot after hours hacking away in the wild, and so by reducing it all to just a few clicks and a number on a bank statement, that gameplay loop was largely invalidated.
Less than two years after Diablo III's release, though, Blizzard eventually binned the Auction House, even if many fans were already long gone.
At least it doesn't seem likely that the impending Diablo IV will repeat the same mistake. Fingers crossed, anyway.