Great little game. Love the fact you took the trouble to get voices in it.
The sprite art is small yet detailed and I enjoyed the zombies frames for their animations. Perfect amount of detail to be cute yet easy to identify.
I did have some issues where my character seemed to stop walking every so often each wave, however.
Some suggestions... as others have said, skip or speed up text button is essential. Waiting for text to scroll is like sitting through the intro of Final Fantasy 1 on the NES back in the day. Which, also, speaking of, I highly suggest you grab some music that is not licensed by Square Enix and Atlus so you avoid trouble by them in the future rather than using the two songs you have now, as much as I am a fan of the game the battle music came from and was glad to hear it.
Second small issue I see with the game is the ice from the panda gets cluttersome. I suggest being able to clear it with your weapon. I mean, eventually, I stood still on days 6 and 7 and didn't need to even attack and she only attacked one side of the screen, but when you are moving it makes the screen filled with ice blocks that take too long to dissolve, making her more of a hinderance than a help, imho.
Last, a small tip, please use the word 'kunai' rather than 'knives' for the ninja chick's weapon that spins around her. It confused me when the upgrade said upgrading her 'upgrades to give you knives that spin around you and makes the knives stronger'. It isn't around you, it is around her, and they are kunai not knives. The difference in the name wouldn't matter, except you have a knife weapon as default weapon 2 and I chose her as my first character, not knowing what to expect with the upgrade system yet. By the way it was worded I thought it meant upgrading her made the damage of my weapon I was wielding increase and getting two knives around my character, not one more of her kunai around her.
Also, if you care at all, you missed a 'P' on 'equipped' under each female you unlock on their upgrade screen. Not a big deal, but figured I'd let ya know just in case.