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 :)