Space invaders on the TT Space Invader in the local gambling hall, 1978.
I held the record (around 163'000 points) when the hall closed on Sunday morning 1am...

Lode Runner on the Apple II, 1983. Great game, amazing as it fit into the Apple's measly ram.

My first game was Nintendo Game&Watch Rain Shower from 1983.

The very oldest game I have played may be Air-Sea War / Battle on Philips Videopac, in US Armored Encounter! / Subchase! on Magnavox Odyssey². That was first published 1978.

On original hardware it's got to be either Space Invaders or Sea Wolf II arcades (though I think it was latter) - both are from 1978, and late 70s is when I experienced them for the first time, so given that was as modern as you can get back in those days, they looked and played great to me.

Breakout for the Atari 2600 is probably the oldest. Also played other 2600 games like Yars Revenge, Centipede, Missile Command and Circus Atari.

These days they'd basically just be equivalent to a minigame on a loading screen or a Wario Ware microgame.

They can be fun but there's no way I'd be able to sit down for a full hour playing one of them.

Super Mario Bros is the oldest game I have played for an extended amount of time in one session.

Atari 2600 and ironically didn't like videogames at that time. Going for the highscore didn't do it for me. Gaming didn't click until the NES when levels become a real thing with a tangible end.

Only old game I liked was Dungeons and Dragons on the Intellivision, first Zelda game made, at least to my knowledge.

I honestly don't know which is the oldest game I've played, won't go checking it now lol, so instead, the first game I ever played:

Prince on Persia for PC (probably MS-DOS I guess, it was some PC, which I saw for the first time too, when I was 5, once, and never saw it again lol)

It was really bad, at the same time I was amazed by seeing and playing my first video game ever, I was also so bad, didn't know how to play at all and even when I got around on how to play it, it was just boring.

I was excited to see a new screen because it was such an amazing thing it existed, but playing it was horrible lol.

Electronic football (handheld). It's shockingly fun, considering it's just tiny lines moving around.

The oldest I played was a console version of Pong. Close to a yellow / burnt orange color with a dial on each wired controller. The first console I owned was a 2600 and I too loved Pitfall.

If we are talking arcade cabinets .... I am not sure I could even tell you for sure which one I played first but I am pretty confident it was before I had the 2600. I remember one of the first being Donkey Kong, Pac-Man, or Tron.

As perhaps betrayed by the OP, mine was Space Invaders on the Atari 2600, from 1980.

Still shockingly enjoyable today, even 45 years later, due to its elegant simplicity.

Probably Space Invaders. My grandfather's next-door neighbor had one of those "cocktail table" arcade machines for it, and I may have played a regular stand-up arcade machine at some point. Arcades were very common in the mid 80s when I was a kid, and the only other games I had access to were on the Intellivision and my father's Commodore 64, both of which are predated by Space Invaders. I never knew anyone with a home Pong machine, and I don't recall ever seeing Pong in arcades anywhere around here.