Games you can't put down? Addictive games? I guess it all relies on what the person, or the user themselves, find addicting. To some it may be First Person Shooters, to some it may be games like candy crush or Tetris.
For me? RPGS. MMORPGS - any "Roleplaying" game with no definitive "End" that you can just keep grinding in. I've always had a soft spot for trying to be the most grindiest in an MMORPG, with max everything to show off. I know it's superficial, but hey everyone likes different things for different reasons. This is why out of all the games I've played in my life I say I've spent the most time on MMORPGS.
Probably since Ultima Online came out in 1997, and Everquest 1 and 2, World of WarCraft, Guild Wars 1 and 2, and more - you name them, I've played them if it falls under that category. Easily 20k+ hours of my life spent in them, if not a bunch more. I'm going with "Bunch more".