A big one for me is Fallout 1. I only played it for the first time a few years ago and it is one of the only games where as soon as I finished it I wanted to start it again. The only reason I didn’t was to play Fallout 2. There is an extremely valid argument that Fallout 2 is better, but the pacing of 1 is so good. It opened up a whole (niche) genre of games I thought I didn’t like, isometric crpgs, especially ones with turn based combat, relatively low player power, and serious consequences.
The other game I could replay over and over again was Metal Gear Solid 1. In my opinion it is the best in the series relative to its time of release, if that makes sense.