A game that didn’t live up to the hype, or a game that you were really excited about but lost you, or a game that took a weird turn in the story that killed the joy?
I immediately think of Watch Dogs. It had a cool premise, and started with cool gameplay, but was totally ruined by the repetitive enemies whose only difficulty increased by the their hit bar getting more and more implausibly larger. A gang member with no armor taking 400 headshots a still fighting was just stupid.
If I have to pick one, it would be Diablo IV. I did have a lot of fun playing II and even III with some friends but we were so dissapointed with IV that we don’t even talk about it anymore