Atari my dad was into Super Breakout, Battlezone, and Combat. He had high score competitions with my grandfather (a career Army man and Vietnam vet) on Battlezone... I was too young to remember them but from what I was told they were pretty intense!
Later when we got the NES I borrowed Solar Jetman from a friend, and my dad instantly fell in love with it! It was so bad I could barely get time on the game (even though I was much better at it than he was :-P). We went out and got a copy a week after I gave it back to my friend, and we hardly ever bought NES games, I always just rented them, so that was a big deal. My dad LOVED Tetris, both on the NES and Game Boy, and also Choplifter II on the Game Boy.
On the PC he was big into Sid Meier’s Civilization, especially CivNet and Civ II. He’d play those games for hours! And of course MS Solitare games on the Entertainment Packs; he liked Tri Peaks the best I think.
My dad was quite the gamer for a long time, until his MS got too bad for him to play anymore. He passed away several years back from complications related to it, but if it weren’t for him I don’t know if I would have had as big of a passion for video games as I do today.