This has been a recent thought of mine that others may be able to relate to—what is my favorite game or game series I've yet to play? Or, maybe others can't relate, and I'm just someone who oddly doesn't pursue to play games which interest them.
With that said: Perhaps you don't own the game system? The game wasn't released in your region? Is there a language barrier? The game's market value has surpassed your spending comfort? Or maybe you just haven't gotten around to it?
For me, my favorite series I've yet to play is Boku no Natsuyasumi. As a franchise exclusive to Japan, it is simple enough that those unfamiliar with Japanese can still play and enjoy. Despite its low language barrier threshold while also having an elementary knowledge of Japanese, I just haven't gotten around to playing any of the games. So, until that time, I'll continue to appreciate them from an onlooker's perspective.