Currently Online 
Halo: The Master Chief Collection - this collection has freaking everything and enough developer made and community made content to last an eternity
Skyrim - this game is over 10 years old and STILL has a ton of people playing it (including myself) and new mods constantly being made
God of War (2018) - this game is so freaking good, I would be more than happy to replay it for a long time
The Legend of Zelda: BotW - Over 5 years later and people are still finding new things you can do in this game!
Pre-Warcraft III Reforged version of Warcraft III - I will forever be salty that Blizzard ruined the, in my opinion, greatest RTS game ever created! The campaign was awesome, multiplayer, and the endless amount of custom games there were to enjoy!
I will say that Starfield may very well replace Skyrim on my personal list I can forever play because I love Sci-Fi and the thought of Skyrim in space may very well be everything I could need.
