that intro is very, very good. it adds a lot of charm to an otherwise simple game. same with how crabchan taunts you as you tackle a wave, it's not needed but it adds personality.
as others have said, i think the back-to-back waves get tiresome. since it's 15 waves, every 5th could be a boss encounter of some kind - just something to break up the standard pattern.
your art style is very charming and nice. i'd totally play a bigger game with art of this quality
keep up the good work