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It could be argued that the biggest impact the Xbox 360 has had on videogames to date hasn't been any single game or technical advancement, but the Xbox Live achievements system built into every game released on the platform. The idea of special or hidden objectives for a game is hardly new, but tying them into a global account score has created an overwhelmingly popular addiction for many Xbox 360 gamers.
While a few games have fiddled with smaller-scale achievement systems of their own (such as Team Fortress 2 and Call of Duty 4), they often feel small in comparison and not as compelling. That's definitely not the case with the new achievements system recently introduced in World of Warcraft alongside the launch of the Wrath of the Lich King expansion. In many ways, it improves on the concept we've come to expect on the 360, adding a wealth of stats and other features that are great to fiddle through even if you never pick up a single achievement.
The main achievements screen is bound by default to the "Y" key, and brings up a list of categories, and overall score and recent achievements. Here's the main screen for the Death Knight I started last week -- as you can see, there are categories for everything from quests and dungeons to professions and PvP:
