For actual video games, mostly just Mario stuff. Like the Mario Kart and Mario Party games. Hell, even today I still watch plenty of YouTube gameplays for them.
For online games, I was addicted to Habbo and Toontown each for years. Habbo, I'll admit I still get on from time to time but only because I'm trying to sell furniture, get coins and then eventually sell my coins for $100.

As for Toontown, I dropped that a while back. I tried playing it on Toontown Rewritten for a bit but then I got bored once my friends gave up.