Depends on the game. Just like some modern games will hold your attention for longer than others. There's some retro games I still clock up a great many hours on.
Pac-Man and Tetris are still my favourite all time games. Doom 2 is still my favourite FPS. Soulcalibur on the Dreamcast is still my favourite beat em up. System Shock 2 is still my favourite survival horror. All of these games were released > 20 years ago (30+ in some cases).
Great points. Also you can dip in and out of Doom quite easily - the original’s three episodes (or five if you include Thy Flesh Consumed and Sigil) can each be comfortably finished within an hour so starting a new game isn’t necessarily a huge investment of time. You also mention System Shock 2 - which is arguably better enjoyed second or third time round.
Pac-Man and Tetris are still my favourite all time games. Doom 2 is still my favourite FPS. Soulcalibur on the Dreamcast is still my favourite beat em up. System Shock 2 is still my favourite survival horror. All of these games were released > 20 years ago (30+ in some cases).