Skyrim is a classic.
Rimworld is really addicting too.
Minecraft also a classic.
Apex Legends is fun.
Personally though, the best singleplayer game I have ever played was a small indie game called VA-11 HALL-A. Beautiful soundtrack and I really dig the cyberpunk pixel art aesthetic, and the story and characters are really interesting. Pretty much the perfect game for me; I don't remember ever feeling so engrossed in a game.
TL;DR of the game - you are a bartender in a cyberpunk world.
Stardew Valley is also really nice for just relaxing and having fun. You'll probably have heard of it.
ABZÛ
and
JOURNEY
are two beautiful games that have no dialogue but completely immerse you in their world. The controls are simple but the visuals are GORGEOUS, and you are almost guaranteed for an emotional trip. These games have a really good grasp on evoking feelings from you, sometimes may even make you cry. Definitely shows the artistic medium of video games.
HYPER LIGHT DRIFTER
A beautiful game in both visuals, storytelling, and music, the gameplay is smooth and very enjoyable.
KINGDOM SERIES
I realise that there are probably too many pixel games here but this one is also really fun, for the same reasons above.
GTA V, no-brainer.
METRO SERIES
As someone who read the books before playing the games, I really recommend the book. Very thoughtful and well-made. The games are great too, they have good mechanics, graphics, and the story is amazing.
THE WITCHER 3: WILD HUNT
Amazing game, immersive world and characters, beautiful graphics and fun gameplay. The story and lore is amazing, all in all really good quality and you will not be disappointed.
If you have a close group of friends, you can play games like
DUCK GAME
is a really niche but fun party game where you just fuck around with your mates and fight each other.
BAROTRAUMA
a horror/simulator game where you and your mates run a submarine and complete various sidequests. The fun lies in the process of doing them because all sorts of weird shit happens; you could get attacked by aliens, or one of your mates gets infected and turns into a zombie, or you can be a sussy baka and inject alien blood into your crewmates and give them psychosis. Alternatively you can just give yourself psychosis.
Pummel Party is also really fun.
If there are any other genres of games you want recommendations on I will do my best to help you!
edited for formatting