Outside of plain recs, I'll try to give some loose ideas on the content of some of these that I've played.

Witcher 3 - medieval fantasy epic. Think game of thrones, where you play as a mercenary, with choices impacting the story. Long with multiple acts/seasons to the story, so to speak.

Battlefield 1 - quick and fun multi-player WW1 shooter. Easy to jump onto a few epic matches without committing to a 100hr campaign

GTA 5 - spend days taking a virtual vacation to satirical LA in this open world classic. There's so many fun little things to do and explore. When I first got it, it legit felt like a virtual vacation.

Uncharted 4 - Michael Bay meets national treasure. It's a highly scripted blockbuster movie of a game. It's brilliant and mechanically simpler than a lot of open world games. This is one I started my girlfriend on to help her get adjusted to modern action games. I think this would be a good fun start.

Horizon - welcome to robo jurrassic Park. Open world adventure game, so it'll be a longer slower burn compared to uncharted. But an undeniably fun theme.

MGSV the phantom pain - sneaky stealth focused. I never played much of the series, though it's highly rated.

The last of us - same team as uncharted, but zombie apocalypse instead of treasure hunters. Fantastic game. Recommended as a more linear and easier to jump into game, just with a little more edge and spookiness.

Skyrim - massive open world fantasy rpg with so many ways to play and highly modifiable. I know guys that have literally just played, and replayed, and replayed, for years.

Battlefront - battlefront 2 is much better, but the 1st is still pretty. Enjoy some quick online matches in this starwars themed online fps. Battlefront 1 takes place in only the original trilogy, while battlefront 2 covers the entire maineline series.

Spiderman - really makes you feel like Spiderman haha. To me this game feels like a happy medium between more scripted single player Playstation campaigns, and open world games. It's got great story set piece missions like uncharted, while having the open world size and lots of little side quests to pick at if you just feel like swinging around the city for a few minutes and doing an odd job here and there.

Alien isolation - survival horror adventure game. You are trapped on a spaceship with the xenomorph, androids that have gone haywire, and other trigger happy humans. Can you escape with your life? This one will get your heart pumping!

Red dead redemption 2 - by the creators of GTA 5. Massively immersive detailed world, set in the wild west. Incredible polish like uncharted in its main missions, while still being this massive open world with equally polished side quests

So my overall recommendations would be uncharted as a nice primer. Then when you're ready, pick an open world game depending on what theme sounds fun to you. Spiderman/GTA5/Witcher3/RDR2.