Breath of the Wild.

I second that.

But I did consider choosing Astral Chain.

SM1/Duck Hunt cart. First Nintendo game I ever played and owned. Never gets old.

You didn't mention any restrictions, so I assume multi-player PC RTS game is fine and would always be able to do team battles or other variations with others. I would go with Startcraft II because I am not very good at FPS games and multiplayer generally beats single player for replay value. There are other decent RTS games, but some reason I always go back to SC2.

I put the entire Saturn/Dreamcast library on an SD card. HA!

Grand Theft Auto V. The pure scale of it mixed with sandbox elements (and gameplay) would keep me entertained for a while. Even if I complete it several times, I could just play it and mess around in the game for fun. There so many mods for it too like an offline co-op mode.

Advance wars dual strike. I can play the different modes forever trying to improve my score. One of the few games I get constant wishes to replay.

Super Metroid.

animal crossing new leaf ngl

Hearts of Iron IV, including some mods.

Those could keep me busy for years, especially the TNO mod