Here are mine in no particular order
UFO: Enemy Unknown
The first game I ever bought so it should be the first game on my list. A turn based strategy that put you in command of the planet earths defence against the various alien species. The ability to build a base, customise your troops and research new techs made it plenty of fun and extremely repayable. It Rocked!!!
Gears of War
Great Graphics and Gameplay gave you the feeling that you were in the heat of battle on the alien world. Superb multiplayer that Iíve been playing since the game first came out to now and Iíll probably keep doing so for the months to come. Also you can chainsaw your enemy and get there blood splash on the screen!!! (Iím a bit sadistic I know)
This game kept me from sleeping for weeks, a good single player mood with a decent story but it really shined when playing with lots of over people on multiplayer. Like an MMO but it was free and gave a better gameplay and easier control than others.
Elder Scrolls 4: Oblivion
Free roaming with more storylines than a Soap opera (but obviously better ones) this game can keep even the most fickle of people interested for months. A highly enjoyable RPG with an excellent combat and character creation system. Great graphics that just make you say wow when walking around Tamriel and see the capital from a distance.
Star Wars: Knights of the Old Republic
The obvious one of the list if only because of the forum this thread happens to be in. Great story with a twist that rivals ĎNo, I am your fatherí and with the ability to make it so you can play it a hundred times without ever having the exact same experience. The greatest Star Wars game to date with a sequel that didnít quite match up to its predecessor but was still good and kept true to the original.