Hmm, interesting topic, well, here's my list with my pointless reasons:
5. Pokemon Silver/Gold (childhood classic, red, blue, and yellow just didn't do it for me)
4. StarCraft (first strategy game I ever played/continue to play)
3. The Elder Scrolls IV: Oblivion (really got me into the whole open world thing)
2. Tales of Symphonia ( first time I really paid attention to the story of a game)
1. Counter Strike 1.6 + Source (reason I started PC gaming)