This is a great puzzle game. I think it actually teaches the concept of "piece coordination" in chess very well.
One suggestion is to have all enemy pieces move simultaneously. I expected that the losing condition is that I am threatened and there are no unthreatened squares to move (checkmate).
However, since the opponents move one-at-a-time, I found that even if I moved to a safe square, sometimes I could be both threatened and captured in the same move! Which is somewhat different from normal chess, since now you have to consider the possible orders in which the opponents move. So even moving to unthreatened squares could be a game over.
You can click your own piece and see the move order to see if it's a possibility you'll be moving into a discovered attack. You can sort of predict that pieces will move if they can go from a non-threatening state to a threatening state.