Game: Treasure Abyss

A common criticism "core" gamers level at Facebook games is that they are fundamentally unchallenging. Beyond the threat of your crops withering, there's no way to fail. Instead you can only be set back somewhat. Whoever designed Namco Bandai's Treasure Abyss seems to have taken these complaints to heart, because this is one of the very few Facebook games in which you can die and have to start over. You can also easily end up in situations where you can't really make any progress until you convince a friend to join you in the game.