Are we talking about positive feelings invoked by the mechanics, like what Paul was saying about satisfying optimization, or positive feelings felt in character? Or both?
Do you need a problem/sadness/tragedy to overcome to get to those positive feelings? If the game is all good stuff, is it hollow/saccharine?
This is a fun challenge!
The best I can come up with is a game of forgiveness. Old friends or lovers who reconnect after 10 years. If the heartbreak is far enough in the past, maybe you won’t have to feel it? (yeah right)
Maybe world-building style games where we build on each other’s contributions, like kids building legos together?