Well, you can take a look through history to see what some people's first games were. lol
Tic-Tac-Toe
Made for computers back in 1952, so I'm sure you could pull that one off.
Blackjack (Twenty-One)
Made for computers back in 1954.
Checkers
Made for computers back in 1956.
Table Tennis / Pong
The first game was in 1958, later inspiring Pong in 1972.
Mouse In A Maze
This might be a bit higher in complexity, but writing maze creation and maze solution algorithms is fun. Oh yeah, made in 1959.
Spacewar
One of the most inspirational computer games, made in 1962.
The Oregon Trail
Made way back in 1971. We're starting to move up in complexity. lol
Maze War
The first FPS (first-person shooter), made in 1973.
Space Invaders
Hit arcades in 1978.
Intelivision
Not a game, but the system had lots of sports games in 1979, so putting sports games here. lol
Pac-Man
This classic came out in 1980. From personal experience: it's deceptively simple.
Donkey Kong
This arcade hit came out in 1981.
Tron
The game based on the movie came out in 1982. I always loved the lightcycle game!
Tetris
Created behind the Iron Curtain back in 1984, this was one of my favorite games to brainstorm code for.
Super Mario Bros.
Bundled with the NES back in 1985. Arguably the most famous action platformer ever.
The Legend Of Zelda / Leisure Suit Larry / Street Fighter
These all came out in 1987. You got your action RPG, your fighter, and a smutty adventure game.
John Madden Football
The first of this long-running franchise came out in 1988.
Solitaire
Released by Microsoft in 1990, a staple program in the Windows OS.
Sonic The Hedgehog
Action platformers revved up in 1991.
Dune II
The genre-defining RTS was made in 1992. A couple years later, Blizzard released Warcraft. So... a late-entry-level game genre. lol
My first game -- well, more like a prototype -- was a sliding puzzle. It was super simple, could be handled in various ways depending on your experience, lead me to some interesting reading on Google, and taught me how to solve sliding puzzles (yeah, I was working on a puzzle I had never solved until then). Then I moved on to writing up a bunch of maze algorithms (I didn't come up with them, I just adapted abstracts to GML). Eventually I made a Puyo prototype, then moved on to Tetris after thinking it might be fun to try different ways to code it. Then I moved on to Pac-man as a side project just to see what made it tick. (Unlike Castlevania, knowing how Pac-Man works hasn't made it any easier for me to beat it.) And yeah, my hiatus project is a Castlevania knock-off. Oh, I also have a card game I'm working on, but it's still just a proof of concept. ...Adulting with ADHD sucks.