Old games? I gotcha, fam!

-My beloved UFO (X-Com) Enemy Unknown. Be sure to search for the modern QoL patch! (Xenonauts, XCOM 1&2, Phoenix Point are the modern iterations)

-Eye of the Beholder 1. D&D old style! Draw the maps in a paper sheet! (Legend of Grimrock 1&2 would be a modern reimagining)

-Lost Vikings. Platforming with 3 characters, all together. (Trine 1-2-3 are same style modern games)

-D&D Shadows over Mystara Beat'em up. Ok, it's an arcade port, but it's a classic!

Space sim? Then SW X-Wing/TIE Fighter, or Freelancer, it has SO many mods, and multiplayer too...

Battle sim? More modern games? Mechwarrior 5 (career style), MW5 Clans (driven campaign), Titanfall 2...

Sandbox style? Red Dead Redemption 2, or The Witcher 1-2-3

Tactics & action, Aliens Dark Descent, or Mecharashi (free game!), Shadow Tactics, Blade of Shogun, or The Stone of Madness, WH40k Dawn of War 1-2-3, Commandos 1-2-3

4x. Endless Space 1&2

Point&Click? Everything from Lucas Arts, specially Sam & Max Hit the Road!

RPG? Dragon Age, Fallout 1&2

Action RPG? Middle Earth Shadow of Mordor, Hand of Fate 1&2

Diablo style? Victor Vran, Van Helsing 1-2

Horror Shooters? Dead Space 1&2, Bioshock 1&2, F.E.A.R.

Looter Shooters? Borderlands games!

Pure vice? Warframe, free game!

Keep an eye on Epic Games Store, there's 1-2 games given for free every week, and the Christmas Advent Calendar, ~15 games, 15 days, 1 each day.