You are Isaac, a naked little boy cast into the network of cellars under his house after God commands his mother to kill him. Unlike in the Bible, no stay of execution awaits you: only level after level of top-down, randomly generated dungeon, populated by Isaac's monstrous former siblings.
You move and shoot in four directions, like a weeping, terrified Robotron, and at the end of each level is a boss. Along the way, if you're lucky, you'll find upgrades that make the going a little easier. Die, however, and it's all lost: this is a roguelike of a traditional sort, the kind that's far more about failure than it is about success.
Isaac is the brainchild of Super Meat Boy co-creator Edmund McMillen and Florian Himsl. SMB threw you under a bus so often that your keyboard had teeth-marks on it, but it never put you in a situation that a little patience and skill couldn't see you through. The Binding of Isaac has no such qualms. It doesn't need to throw you under a bus, because the bus is being driven by driven by a madman who holds you personally responsible for all that's wrong with the universe.
McMillen's signature body horror is a natural fit for a genre where the slightest error can cost you everything. Isaac is grotesque both in design and subject matter: Isaac's initial weapons are his tears, with which he fends off oncoming hordes of bulbous infants and bloated flies. An upgrade might pierce Isaac with a coat-hanger, or embed a third eye in the back of his head to enable him to shoot backwards. Between stages, Isaac's dreams show him being humiliated by everyone he knows.
It's a broader-ranging expression of McMillen's interests than we've seen before, drawing on The Legend of Zelda, Bomberman, and Ren and Stimpy as well as the Old Testament. The unifying theme, if there is one, is childhood: but this isn't a game on a mission.
There is, however, an intelligence to The Binding of Isaac that prevents its excesses from ever becoming crass. Instead, the relentless cruelty of the game is a joke that invites you in but asks you to see it for what it is. Firing it up for a single run-through quickly becomes a refreshing aside, a willing engagement with a world that is unfair, nasty and short and doesn't care to hide it.
The genius of the game is that it grounds the roguelike in a context that is as meaningful as you want it to be. Whenever you curse the game for delivering you into a no-win scenario, the temptation is to blame the unseen hand that hates you so very badly: and it's then that it hits you that there isn't one. The Binding of Isaac is a piece of software, made by people, and it is neither out to help nor hinder you.
The game's nature will divide some and outright offend others, of course: but that's exactly as it should be. A worthy, compact and highly enjoyable experiment.