I would have immediately forgotten that some people on the Internet weren't fond of Diablo III's art direction way back when, but then Blizzard turned the would-be drama into something that the rest of us could laugh about. The joke has gone a step further and materialized into a full-blown secret level.
Between the cupcakes, rainbows, smiley faced clouds, unicorns, and all the colors you could ever want, Whimsyshire sure is a magical place. Instructions on what's needed to reach the level can be found here. And here's an alternate video showing the entrance for good measure. Nicely done, Blizzard.