By Jo Walton.
Well-written but it becomes melancholy partway through, with practically inevitable doom resulting from a serious curse for what seemed like a wrong cause. There were some irksome typos ("how at" instead of "at how", "than" instead of "that", and so on) which suggested hasty publishing, though.
I have put off reading this book for at least a year, probably, since I read The King's Peace and The King's Name, because I knew at least some of what would happen to the characters in this book and didn't feel like getting to know them better. (This book concerns some events befalling certain characters before they appear in Sulien's books.)
This has much of the same flavor, but is perhaps narrower and less majestic. Sulien's story is hard to top.
The author's note at the beginning says that a candle casts a shadow both backwards and forwards, but I think I might recommend reading this before The King's Peace and The King's Name, although for the same reason you might arguably read them the other way around: certain events in those two books will change the way you look at Conal and Emer. I also have sympathy for Elenn; Maga is a horrible mother (and king) but forcing Elenn to marry four husbands in as many days is even more appalling than usual. It leads to some saying she bears a curse...
Worth reading if you read The King's Peace and The King's Name, too, either before or after. I don't think it would stand very well by itself; although The Prize in the Game is quite understandable on its own, I don't think it's worth reading without the greater context provided by the other two books.
Incidentally, the title refers to a kingship, but it seems to be almost a trivial matter, mentioned halfway through and not referred to directly again. I think the cost of winning the game is far more than the one who wins would ever have willingly paid, but the narrative never says that explicitly. The last (one-page) chapter is also somewhat ambiguous: is the last line casting judgment or only noting a simple truth?
Update: The other thing I wanted to mention was how every warrior knows charms to heals wounds, prevent "weapon rot" (blood poisoning), reattach limbs, etc.--as long as the weapon that dealt the wound is available. Consequently, they all tend to come through battles either alive and with very few consequences or permanently dead. Almost no one in these books dies slowly. They take fighting very glibly as well, and that's part of the reason these are melancholy; diplomacy is not much employed and often enough you end up fighting against the side your friends are on. I think the consequences of a system like that in the real world would be horrific.
I should also mention their suspect beliefs about fertility: women are not fertile before their wombs are opened by a priest when they get married, and not wanting a child can cause a miscarriage. (Admittedly the first one is proved wrong more than once in Sulien's books, so I guess not even they believe it entirely...)