Kids these days ... sigh. I singed up to post one word.
Zork
Okay, a few more words.
Total Annihilation is by far the best RTS game, ever.
Total Annihilation is an incredible example of an RTS, still played today in multiplayer, with many videos on Youtube.
Some other defining games that I have played would include Dune 2, Diablo 2, Fallout and the original Deus Ex. But I can see why modern gamers wouldn't go near them today.
For more modern games worth a play, and based on what I own, I'd suggest:
XCOM2 - stylish, tactical gameplay with mod support.
MGS V: TPP - an unfinished game but still enjoyable with good graphics.
Skyrim / Fallout 3 / Fallout 4 - to learn about mods.
Mass Effect 2/3. It's a pity that the first game is a little more difficult to get into for newer gamers, but it makes 2 and 3 so much better. The suicide mission in 2 is magnificent, as was the Lair of the Shadowbroker DLC.
Dishonored - a beautiful sneaking game. I didn't like the sequel.
Deus Ex Human Revolution - a more modern Deus Ex. I didn't like Mankind Divided.
They Are Billions - a devious but addictive RTS. Unfortunately it stopped working for me months ago.
Battletech - a modern version of a classic tabletop game.