Mission in Snowdriftland is an absolutely gorgeously detailed 2D side-scrolling platform Flash game with production values that rival Nintendo's own efforts in the category. In fact, this one appears to have been commissioned by Nintendo as an advergame as it contains all sorts of delightful unlockable goodies—from screenshots and wallpapers to videos and ringtones—from several of Nintendo's latest DS handheld and Wii console offerings.
Beginning with a lengthy intro cutscene that develops the game's background story, you learn of a terrible plot in Video Game World by El Pix who has stolen important game files from a laboratory and retreated to remote Snowdriftland. Chubby the Snowman gets the task of recovering the files and off you go.
The game overworld is presented as an advent calendar with each of the days of December leading up to Christmas representing a playable level that, when completed, will unlock the files for the featured product. So far only the first 8 levels are unlocked with a new level being unlocked each day.
Cheers to Wouter for the heads-up about this exceptional game. =)
Update: Unfortunately, this wonderful experience was short lived as extra toxic has taken the game offline. They tell me they will continue to make exceptional games like this one, and that you may even see another game based on the game engine used for Mission in Snowdriftland.
Update (Dec. 2010): IT'S BACK!