Topic.
In my opinion there are two other games that are more influential. Halo: CE and Grand Theft Auto III.
GTA 3 literally changed the landscape of gaming. It created the first truly engaging sand box on a console.
I like Halo more, but GTA 3 was the most important game of the last decade.
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Yeah, GTA3 and Halo were more important, but they're just outside of the timeframe. I'm really surprised Resident Evil 4 wasn't included. It basically set the mold for modern third-person shooters as we know them nowadays, and it's also a great game with fantastic level design and pacing that has yet to be rivaled. I don't think Half-Life 2 was all that important in the long run. Great game and I love it, but it didn't have the impact of something like RE4, WoW, Wii Sports, or Call of Duty 4.