Why not just mention the Witcher 3 or For Honor, if we're going to take that easy route?
Gameplay and game controls haven't evolved since dual stick controllers became the norm. Any game that was good from the PS2 and onward should still be considered good now, if you can get over a game not having the prettiest visuals.
Finding a 3D game on the N64 that a kid used to dual sticks could get into, is the real challenge.
On the PC we've been doing keyboard and mouse controls for ages, but if you go way back you can spot changes in design philosophy or improved GUIs for different genres that make a big difference.
Base RTS:
Dune 2 was very clunky, lacking many shortcuts, queues and group commands we're used to now, but the young genre evolved fast and C&C already had most of the functions we now expect in place. The genre continued to evolve, but a recent game like SC2 is actually a step backwards in terms of GUI functionality and streamlining from an oldie like SupCom. Many (SC) players don't demand all the conveniences and are willing to do some repetitive, mundane tasks. Nothing happened after SupCom.
Any old answer up till SupCom works, but I doubt anyone without nostalgia goggles, would find beating Dune 2, Warcraft 1 or AoE 1 worth the bother nowadays. It's a very big leap from WC2 and AoE2 back to the originals. For me, SC1 is still a good game, but for the pioneers, a lot of the original appeal was just novelty and unreached potential.
Puzzle AG:
The designs of the old text AGs like Infocom's and the early graphical AGs relied on trail&error, dead ends and restarts and the purpose was to challenge the player for a very long period of time. Fairness wasn't much of a consideration in puzzle design and the pacing of the story was non-existent. After that came two distinct, popular variants: Lucas Arts style AGs that did away with the dead ends and made solutions require a little less moon logic and Puzzle box AGs such as Myst that featured series of self-contained, logical puzzles. The first variant eventually reduced most of the distinct commands to just look, operate/take and use an inventory item and the second evolved to include games that are a series of rooms with physics simulation based puzzles.
Here it mostly comes down to tolerance levels. A player who can handle BouT I would expect capable of enjoying old Monkey Island and if you can do the Talos Principle, Myst should be at least palatable.
MI1 holds up, but so does Leather Goddesses of Phobos and the best personal answer here would be finding the oldest true classic that doesn't overcome your patience, willpower and stubbornness.
