Heh, my thing is that I act like I have ADOCD (Attention Deficit Obsessive–compulsive disorder) I know quite well I don't but I can be addicted to a game for a while then just not even want to touch it sometime later.
Guess my first one was Runescape, dark part of my life that was, looking back on the game now it... Well it sucked, all I did for a good 60% of that game was chop trees, lost a good 3-4 months in it.
But it was my first MMO that I ever played so that's something I guess.
Next came World of Warcraft, this one... Dang, lost count how long but I guess a year or so. Don't think I need to explain why.
There was a time from WoW to my next one where I still wanted to play MMO games but didn't want to pay for it, tried a lot of free-to-play ones before I found my next hour waster...
Guild Wars, ok this was some of my best times in a MMO ever. The game was fun, didn't have any of that mining or crap like other MMOs, a vast amount of PvP that I loved (Alliance Battles = Awesome!) and a great story. Sadly I grew board of the game after about a good year and a half, that and ArenaNet &%#@!$ the game up so much with all the patches and "Class Balance" (Like the Ursan Blessing nerf) that most of my friends went on to other games, as did I.
After that I dabbled in some other MMO games such as Shaiya and City of Heroes but nothing ever really went over 3 months. As for non MMO games... Waaay to many to post in here but the biggest ones are DOOM, Diablo, and The Elder Scrolls Games.