It was kinda cool, love the idea! However, I'd enjoy a bit more control over my pieces, watching them making bad moves automatically and interfering with eachother took most of the strategy out of the game imo (please don't let your game become an "autochess" game :) ). Anyway, I quickly reached a perpetual winning situation in each game (even in "no" difficulty) and finally left with hundreds of material (I thought I would someday see a whole army of queens coming against me, but no :( ).
Also, why is the king so hated? :( It's one of my favorite piece, i'd imagine him as a very tanky piece but somehow with low attack. Why not include him in a "protect the king" mode? Or even in current game?
The healing mechanic is really what makes the game easy and in the end it's what you do during almost all your turns (which takes the fun away). As the knight and the bishop seem pretty similar to me (also kind of useless btw), why not somehow make a healing mechanic with the bishops instead?
- upgrades (health, damage, new spawning tile, number of actions per turn...)
- control over your pieces (as mentioned above)
- collectables (resources/healing/offensive spells) on the chessboard. Collecting them would be a great job for knights/bishops as they are pretty weak but have some mobility (whereas you can't afford to not use queen/rooks in combat, and pawns are too slow)
- obstacles / different maps
- new pieces ? making a game with a (imo underexploited) damage/health system is a great opportunity! I want to see cannons, catapults, archers, wizards, clerics, paladins, walls, spearmen :D