The rating "mature" can be applied to any game with a gratuitous amount of violence, cursing, or sex, but Catherine is an M-rated game with a difference: It actually IS mature. It deals with many real-life situations, such as infidelity, obsession, and alcoholism. Series of questions are presented to you through the game (like "Can love exist without pain?") and your answers will determine where you fall on a morality meter pointing towards "Law" (commitment, monogamy) and "Chaos" (a devil-may-care, sleep-around lifestyle.) It determines which girl you'll end up with, as well as what will happen to the protagonist as well.
The game has a lot of language and sexual innuendos. The violence is present, not terrible, though images of men's corpses in their beds are quite frightening, as are the level bosses. However, the climactic scene culminates in a stabbing, with a large blood puddle running from the body.
There are also religious undertones. A painting in the "confessional" where you answer questions features the protagonist crucified to a Venus symbol, and in later levels, a crowd of sheep gathers around him. There are also copious references to Assyro-Babylonian mythology. Such tie-ins create an almost hallowed atmosphere that further enhances the game's dark and serious nature.
The game pushes the boundaries of being a game in the first place and quickly gets under the player's skin and into his head. In the game's opening sequence, a sheep falls through midair onto a cutout of the "double-Catherine" stamp, landing with a bloody splat. It then cuts to Vincent (the protagonist), crucified to a tower of blocks with barbwire, as his girlfriend sits above him . He turns his head to the player, as if to break the fourth wall, and shouts, "CATHERINE!" His cry for help sucks you in - and you didn't even press start.
Once you do, however, the game alternates between animated sequences - beautiful cel-shaded snippets of the story - and the nightmare sequences, which involve moving blocks around in order to climb to the top. I've heard many complaints that the game is frustrating. And yes, it is. If you're especially dexterous you can pick it up in a heartbeat. There is also a "Super Easy" patch that was added to the game due to Atlus recognizing the complaints of Japanese players.
It's deep, it's dark, it's gritty, it's sexy, it's completely insane: delightful in its whimsy and stark in its veracity, Catherine is an experience. It is like nothing you've ever played before and few games are likely to match it. This is, hands-down, one of the best games ever created, and I've been playing since my NES days.