The Daily Grind: Does a game need PvP to be successful?

Player vs. Player combat seems to be a love it or hate it scenario. Players either engage in the behavior with an extreme liking, wondering when their blades will get to silence a screaming newbie or go up against the best of the best in battlegrounds, or players hate the activity with a passion to the point where they'll avoid it as much as possible.

In any case, this feature certainly has become a staple of MMOs, even going so far to have a couple games, like Darkfall, EVE Online, and Aion: The Tower of Eternity, making it one of their core focuses. So this leads to today's question: Do you think a game needs to include some form of PvP to be successful? Or can a game go with a purely player vs. environment or cooperative approach and still succeed?

Drop your thoughts into the comment box below and sound off.