hmm, well, let's start at the beginning...PONG.
And then countless arcade games, and then dozens of games on my Intellivision, and some more arcade games (I don't know HOW many hundreds/thousands of dollars I "invested" in John Elway's Team Quarterback alone!), and then countless games on my C64 (Beyond Castle Wolfenstein, Lode Runner, Pool of Radiance), and some more arcade games, and then Madden Football and Populous on the NES or SuperNES back in college in early 90's (man, we played Populous for hours on end!), and more arcade games, and then I got my first "IBM-compatible" PC in '94, and then Solitaire, and...
...and then Doom just blew everything the freak out of the water...wow...
and then there were all the rest of ID's games, and let's not forget the original Command&Conquer (holy crap was I addicted to that until I finished it!), and who knows what else over the past decade or so...
...and last year, I played nothing but Jedi Knight multiplayer for like 6 months straight (I still have never even tried out the single-player mode on that game!)...
...there, I think that brings things up to the present...oh, well, wait, my loving wife just got me an Xbox for Christmas, so I guess this story of countless addictions is "to be continued..."
(basically, there's no one single game out of my 25-year gaming history that I could label as "most" addictive...there's just too many)