Neat game! It is, as you say, a memory test. The square grid layout lends itself well to this sort of small resolution, I think. It might be useful to somehow indicate on screen when one has pressed space and a new turn begins; it's quite disconcerting to press space to advance a turn and nothing at all changes. It makes me think: did it notice me pressing space at all? Perhaps the game isn't focused? So having some sort of visible reaction to the player pressing a key would be a good idea, although I'm not sure what would be best: a turn counter incrementing perhaps, or a very small quick popup showing that a turn has advanced? But the game is fun even without this. This could be a cool minigame in a larger game, I think.