Every gamer has a story of sitting down with a couch co-op game and playing with friends for hours, and many players bond with their partner through a co-op experience. Co-op games can make a good game even better, but they can also ruin a game that isn't designed for co-op. While there are countless games that have been improved by co-op, there are just as many that have been ruined by unnecessary co-op.
Source：https://www.cbr.com/co-op-games-better-as-single-player/
