Assassin's Creed II Game of the Year edition includes the two missing game sequences and three Templar Secret Locations. All of these additions are available as DLC for the original Assassin's Creed II game release.
"Assassin's Creed II is a third person action-adventure video game developed by Ubisoft Montreal and published by Ubisoft for the PlayStation 3 and Xbox 360 video game consoles, and Microsoft Windows. It is the second video game installment of the Assassin's Creed series and is a direct sequel to the 2007 video game Assassin's Creed. The game was released on video game consoles in November 2009, and released for Windows on 3 March 2010.
The game is set in 2012, with player-controlled protagonist Desmond Miles escaping from Abstergo Industries with an employee, Lucy Stillman, after being forced to relive the genetic memories of ancestral assassin Altaïr ibn La-Ahad through a machine known as the "Animus." After escaping from Abstergo, Desmond enters a device which is more advanced than the Animus and relives the genetic memories of ancestral nobleman Ezio Auditore da Firenze, who lived during the Renaissance period of the late fifteenth century in Italy. The player controls Ezio, who becomes an Assassin after his father and brothers are murdered by a traitor to the Auditore family. While controlling Ezio, the player can explore game renditions of Italian cities, regions and landmarks in open world gameplay. The gameplay is a mixture of action, stealth and platforming."
Source: Wikipedia, "Assassin's_Creed_II," available under the CC-BY-SA License.