The #Forzathon stuff is amazing. Playground Studios are literally the only dev that have done something good with Challenge achievements.
They were initially the most stupid, and pointless, and I'd even say mean-spirited addition to Xbox achievements this gen. Zero-gamerscore, time-limited achievements that added literally nothing, other than encourage you to be an early adopter, and encourage you to not sell your game. Time-limited achievements for playing the game on day one: barf. Staggered schedules for time-limited achievements that stretched out for months and months: barf.
But Playground Studios have done the following:
1) Incorporated the Challenge achievements into the base game in a brilliant/organic fashion: The #Forzathon challenges/requirements/explanations are visible in-game with nifty menus, and all the radio station DJs actually talk about #Forzathon! They actually recorded dialogue for those DJs to hype up #Forzathon... pretty awesome.
2) Provided legitimate rewards for people going after the #Forzathon challenges, like credits, experience, car horns, actual cars, etc...
Good job from Playground all around.