I am so fond of the Joyful Game. I think it's important (especially in the gaming sphere, where things tend to get competitive at best and vitriolic at worst) that we have games that make us more hyper-aware of our positive connections to other people. Having joy in turn makes you want to share joy with other people!! And in the face of seriousness & pain out in the world, our minds need to...in a sense, "fill up with joy" to combat the world! The definition of a Joyful Player is also nice. Could a Joyful Player in turn make any game into a Joyful Game?
I like how the examples of Joyful Games given all embody a similar aesthetic as well: bright colors, pleasant sound design, and friendly shapes! I'd also like to nominate Videoball by Action Button as a Joyful game. Maybe some people will disagree with me, I don't know. Also, I think what makes a good Icebreaker game is similar qualities to Joyful Games.