Most people enjoy the company of other people. Our games should support this.
While a OnePlayerGame is good for when no other players are available, there should be appropriate games for when there are other people around. Besides something to do together, games with social interaction can server a number of purposes: a reason to get together in the first place, or getting to know people better; either as an ice-breaker to deepening the relationship with existing friends.
Social interaction could even be the subject of a game as well as a mechanic; see the SoapOperaMeme.