Left 4 Dead is a game about love.

Perhaps ‘love’ is a strong word, but playing Left 4 Dead on a high level with a team of other players requires all the traits of a healthy relationship: trust, communication, and occasionally self-sacrifice.

While they’re always carrying heavy firepower and an emergency health pack, players are consistently outnumbered and often exposed on several sides. Beyond that they have more than zombies to worry about, there are several ‘Boss Infected’ that each have the ability to completely incapacitate a player.

In short, you can’t make it on your own; you have to rely on your friends.

Altruism is not the opposite of self-interest, of course. It’s easy to do the math and figure out that one player down and out means 25% less force that can be brought to bear on the undead hordes, as well as one less person to carry important things like healing pills and pipe bombs.

However, many of Left 4 Dead‘s best moments rely on more complicated emotions. Such as when a player fires on a group of zombies attacking a friend before turning to defend himself, or when a group hunkers down to help a wounded ally make those last few steps. These are moments that don’t have much to do with a cost/benefit analysis of the situation.

Of course, the same scenarios that present opportunities for heroism also create stages for cowardice. Games can be lost when someone refuses to heal another player, or when they dodge behind another player while still firing wildly.

It might not seem obvious at first, but this game about the zombie apocalypse has a lot of heart. Even without long cut-scenes, text blocks, or dying NPCs, Left 4 Dead manages to be the most meaningful game of the year.