Very good graphics and visual design (it really appeals to me!). Good music too.
Simple, unexpected, smoothly executed gameplay. I'm not sure how well the secondary abilities contribute, but they're cute additions that emphasize individuality of each character.
The use of the "only once" theme seems weak.
The game is basically over if one of your characters die before the final fight. I think having some amount (or even full) recovery between each stage (and adjusting stage difficulty to compensate) would have been more fun.
I think I was taking damage on my own turn sometimes, and I don't know how.