Play it if: you want to read a story you can admire, a short, brutal punch of a game that'll stick in your mind for a long time to come.
Don't play it if: you're out of room in your heart for bleak truths.
How sarcastic I must seem, using such grim terms about a game that advertises itself so lightly.
To be honest, it took me about three playthroughs of Horse Master to really grasp what I felt about it. On the one hand it's a tragedy of desperate ambition, but at the same time it's a snigger-inducing parade of the absurd and the grotesque. Half the time I felt like I was being asked to laugh and cry at the same time, so I ended up doing neither and instead just feeling emotionally mangled.
The story is on the surface that of a person rearing and training a horse for a prestigious competition. The immediate twist is that the "horse" in this case is not really a "horse" as we know it, but appears to be some sort of mammoth crustacean grown from a larval stage. Much of the sheer oddness of the game is derived from the contrast between the glowing, admiring terms in which the horses are described and the true details of their appearance, which are left a little vague but sound anything but noble or graceful to the common reader.
Of course the more important twist is that it's not really a fun, quirky horse-raising sim at all. That's just the foot in the door.
Say what you will in its defense, but to the uninitiated it's not so different. To achieve competitive success as a bodybuilder, a person has to exercise, diet, gorge, dehydrate, medicate, and groom themselves obsessively to warp their bodies into extreme forms. They risk and experience poverty, ridicule, and failure in turning themselves into something that is ultimately decorative. They don't perform astounding feats of strength or agility. They pose.
Speaking purely as an outsider, there's something terribly tragic to that sort of lifestyle, or at least to the way it's seen by much of the world. That men and women can invest so much of themselves into an endeavor which is so often thankless.
As odd a decision it might seem to have the horses not be mammalian, I think there was a purpose to it, and that purpose was to emphasize just how un-beautiful this sort of thing can really be. Some types of dog shows maintain frankly arbitrary and ridiculous standards for their competitors. To me, weirdo that I am, breeding creatures for their aesthetic value to humans is something deeply disturbing and abhorrent - but their aesthetic value often inoculates us to the ethical concerns. In Horse Master, we don't have that illusion. The creatures being bred and displayed are not the kinds of things that inspire joy and awe in the minds of My Little Pony fans.
It's a value dissonance of the kind present in the assassination-training scene of howling dogs, though here its purpose is much clearer: to make us reconsider our questionable relationships with the animals who inhabit our lives.
(Spoiler - click to show)I think it's somehow fitting that the ending will always destroy someone in the balance. Either the player loses everything and has no future outside of poverty and obscurity, or the horse dies in an exploitative, orgiastic display. Either the player character is crushed by a world which does not really care about her existence, or the horse is slaughtered by a system and a protagonist who does not really care about its wellbeing. You're a bodybuilder, or you're a dog breeder. The perpetrator or the victim.
It's not very uplifting. But it is compelling in its own way. And it sort of gives you pause for thought, doesn't it?