Such a lovely concept, and really well executed! This was a pleasure to play, thank you!
Two suggestions for balancing:
First, death is a bit too unforgiving given the length of the game. How about savepoints, or "undo" move (maybe available only for moves that kill you, so if you back yourself into an un-winnable situation you'll still lose, but don't have to lose from blunders alone?). I also frequently died from a key repeat in some direction, and didn't see some piece in time, so maybe a "check!" that interrupts key repeats? Or, like other roguelikes, interrupt key repeats when an enemy is spotted?
Second, the final room was super exciting and appropriate when I first saw it, but then it was anticlimactically over in two moves (although the ending screen was great, and taught me two new words)… I would suggest it more challenging by putting the pieces out of range of a single rook power move. (Or maybe you tried that, and then the room proved too hard?) An undo or a savepoint would have also been fun at the end; I also didn't realize the game would end as soon as the final queen was taken, I kind of wanted to also try first annihilating all the other pieces in the final room, which might be more challenging strategically.
But, having two moves between when a piece spots you and when it moves is, I think, an appropriate mechanism.
And, it's lovely the way it is with, I assume, randomly generated maps. But I can also imagine lots of possibilities for really devious room/level designs, effectively chess puzzles for this new variant of power moves+pawn summons, that could make this have DROD-level depth and complexity.
Thanks for the detailed feedback. It's actually kind of funny reading your comments, because many of them are almost verbatim what dotSamm and I talked about: a "You're about to move into check, you sure you want to do that?" system, enhancing the final boss to be a bit more challenging, a checkpoint/save/lives/HP system, different types of map generation, etc. The only reason we didn't dig into those is because the 7 days we had to build this game from scratch went by surprisingly fast.
However, we are continuing development on A King in Checkxile, and you are asking for the very things we are eager to build :)