Half-Life 2, hands down.
Final Fantasy X - it had a beautiful story (and graphics for the time) and great character development.
I started playing with PitFall on Atari (Damm I feel old!)
Zelda Ocarina of time (N64) got me back in the game world (Will always be in my cherished games... loved Twilight princess (cube) as well).
But Rainbow Six 3: Black Arrow got me to plug a Xbox in my veins! And since then, I am a R6 lady!
-"I'd like to apologize in advance for anything I may say or do that could be construed as offensive as I slowly go nuts!" - Col. J. O'Neill
-"If men had wings and bore black feathers, few of them would be clever enough to be crows."- Rev. Henry Ward Beecher
One? Just one?!
I have spent the most time sunk into Mario games and Final Fantasy, but two games I truly LOVED playing and can play without boredom. . .
DinoPark Tycoon- This was the first game that got me into PC gaming and it was provided through my school. It was released to schools to teach children skills that could be used IRL but truly. . . it was a pc game with MF DINOSAURS!
RoadRash- There was just something about being able to ride a motorcycle while whipping people with a chain that brought me endless hours of unproductive fun.
I think it's Close Combat 3 for me.