Halo 2
Halo 2 was the most popular Xbox Live game on its release. It held that title until the release of Gears of War nearly two years later. By June 20, 2006 over 500 million games of Halo 2 had been played over Xbox Live. It was, and still is, the best selling Xbox game of all time with over 8 million copies sold worldwide. It broke sales records in the US, many of which were only broken by its sequel Halo 3 in 2007. The Windows Vista version in 2007 was less successful as the fact it was released 3 years after the Xbox version gained many negative reviews.