MS Solitaire, Space Pinball, and Minesweeper come to mind. They were not my favorites, but I know a few people who have a few hundred hours on one or more of those.

For me it's C&C Generals Zero Hour. I have had a copy since it released in 2003, it still works, and I still play it in single player mode at least once a week. It's great because it does not require a huge time commitment and campaign missions take about an hour or less to complete. To me it's one of the best RTS style games out there. My second favorite? C&C Red Alert 2 and Yuri's Revenge.

I have also very much enjoyed the Assassin's Creed series up to AC Odyssey.