Can a game stand the test of time long enough to define a decade? I doubt it. Many innovative games have been released this decade, but they usually become nothing more than a great sequel a few years later. There isn't a fair way to compare a game that was made in 2009 with a game made before 2005. It's hard enough trying to compare a game to it's predecessor. Put Grand Theft Auto 3 next to Grand Theft Auto IV and they both look dated when compared to a game like Assassin's Creed 2. Graphics aren't everything, the Wii proved that, but they do increase a games chances of surviving the test of time.
We're at the point of the cycle where most of the original IP's released this generation have sequels. Should we ignore predecessors and give the award to either a game without no sequels or the latest game in a franchise? I'm sure there are people who feel that both Uncharted 2 and Assassin's Creed 2 are not as good as the originals, but sales say otherwise. Do sales matter when it comes to determining the Game of the Decade? If so, then Wii Sports should be a contender which is an insult to gamers.
If the award was divided by genre, how would the Sports Title of the Decade be determined? Would it be the 2010 (2k10) edition because of the latest features, or does the roster at a certain year determine it's dominance? Since Madden has been the only NFL game since 2004, should we consider Madden to be the NFL title of the decade?
It's hard enough trying to compare a game released in 2009 with a game released in 2008. When a game is new, it represents the year it was released. Look at Fallout 3 and Borderlands. Both games, released a year apart, are First Person RPG's set in a wasteland. Fallout 3 uses the setting to complement the dark theme about Washington DC after a nuclear war. It was released in 2008 when the economy was beginning to really suck, and the future wasn't looking too bright. Borderlands comes out a year later and has a more lighthearted approach to a wasteland. Instead of feeling like a victim to the situation, your on a treasure hunt with funny robots, cool guns, and raiders who don't have bodies hanging outside of their hideouts. Both games have different intentions, but what a difference a year makes. The lighthearted approach this year could be a reason why Mickey Mouse is returning with Epic Mickey next year.