I can't just pick one game so I'll pick 3 series. Forza, mass effect and the first series of Pokemon!!
Gotta be Golden Eye on the Nintendo 64, I played that for about 2 years and had world record times on it
For me it has to be Mariokart on the snes I would not like to say how much time I spent playing that. I still have the game and do play it every now and then.
My favorite game of all time hands down is chrono trigger not much more should need to be said but for those who don't know a legendary SNES game that has everything from time travel to multi char customization RPG at its best #keep the 90's alive