I've been playing jet moto with my kid. Just like I did with my dad, back in 1996.

I still play a phone sudoku game from 2009. I would still play StarCraft and Warcraft 2 if I had hardware capable.

1991's arcade hit and genre creating game, Street Fighter 2

River Raid, Atari game from early 80s. Play it on analogue pocket currently

DigDug on MAME

Portal. It's older than you think, but still solid.

I replayed Vampire: The Masquerade — Bloodlines (2004) recently

Garrys Mod. You'd actually be impressed how many people still play that game for it approaching its 20 year anniversary.

I recently picked up Diablo 2 again, that and Doom which I play off and on. I really need to find a copy of Wolfenstein now that I'm thinking about old games.

The barcade near me has a Sinistar (1982) cabinet and I play it every time I go. I’m not even that good at it, but I love it so much.

Also I love those Lucasarts point and click adventure games. Grew up playing Monkey Island and play it again every once in a while.

osu!. Despite being made in 2007, it still holds up as a good rhythm game.

Mario Kart: Double Dash!!

Every so many years I fire up a King's Quest or Space Quest.

Mario 3, though these days I get tired of it after a World or two and haven't completed it in a while.

Also Xenogears from the PS1 is still one of my favorite games and I replay it every few years.

Thief: Gold

The Dark Mod scratches that itch very well most of the time, but the OG had better story telling across multiple missions

Freeciv

I'm on a retro game kick lately. I am currently playing Pokemon Leaf Green and Chrono Trigger (for a fiesta event) and will likely move on to Castlevania: Symphony of the Night afterward.

I play lots of games from my childhood. Even though it was before my time, Super Mario Bros on the NES is probably the oldest game I regularly go back to. But I love retro games, so I'll play even older games on occasion.

Joust.

Mario 64 on original hardware. Never did finish it as a kid so no time better than the present

Bejeweled 3 zen mode on my Xbox 360 till my Xbox one X

Regularly Cube2:Sauerbraten, initially from 2004.

Occasionally, Dragster on Atari,1980. Some of the best reaction gameplay available, from the golden years.

I still play NES games often. These were the games of my childhood. Balloon Fight and the original arcade Mario Bros. are always fun for shorter sessions. And I still enjoy playing through Super Mario Bros. on occasion. I very rarely have ventured into games older than the NES.

I'll only stop playing OSRS if they shut the servers down.

Anarchy Online (2001) is a game I play frequently.

Last three were Star Ocean (the first one), Radiata Stories, and Skies of Arcadia.

Currently playing Alundra because a friend grew up with it and wanted me to play it. Honestly it's not great but RetroAchevements made the bosses extraordinarily painful to master, which is uh ... fun. Yes. Fun, let's go with that.

Oh and ps these commenters all have fantastic tastes.