It's dangerous to go alone!

Lovers in a Dangerous Spacetime is a really great example of a game that could be played seriously, but is still fun in a haphazard party. Like New Super Mario Bros. Wii or 3D World, in that sense. Also there are space lasers. And space flails.

Lovers does lean a bit more toward the "hard" angle, though, which makes it more difficult to enjoy once your party - disorganized, or drunk, or both, as they may be - hits the wall. Restarting from an unexpected death is not as convenient as in Nintendo's genre experiments; and so it's harder to learn from your mistakes, since you have to re-do a lot of the level just to get to those mistakes again.

It's a very cool idea, though, and one I look forward to trying more in the future.