A lovely game, I would suggest two changes, make it so that the game restarts on whatever wave you died on (if there's only two waves it's pretty much a non problem, but if you added more it might be), second I would make it so when you are injured and invincible you can still parry/attack, this allows the player to bootstrap their way back up, as it is you have to wait for it to wear off, and then block the next attack.
That being said very much enjoyed it man!