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Stray comes to mind. Once I beat it I haven't picked it back up. There's a few games I've played since childhood that I tend to pick back up from time to time such as the Genesis Sonic games and even Generation 1 of Pokemon. I love going back and playing games I beat as a child.
 
There wasn't anything that I felt the need to go back to the portal series after I finished it. The thrill and satisfaction gained from beating the puzzle challenges were just enough.
 
Stray comes to mind. Once I beat it I haven't picked it back up. There's a few games I've played since childhood that I tend to pick back up from time to time such as the Genesis Sonic games and even Generation 1 of Pokemon. I love going back and playing games I beat as a child.

The Pokémon is a great franchise with lots of interesting games that one wouldn't get tired of playing. I've played a couple of Pokémon games twice after playing it for the first time.