OK, I gave it a run through.
I actually never played one of this sort of game before (for one who enjoys making games, I have surprisingly little knowledge of most popular games and game types). So here's my impression...
It was fun at first, but not enough variety to hold my attention for long. You were right about sounds, they would help a lot.
To my surprise, I liked it a lot better after the poop "died"and became a punk. The punk-poop was funny and entertaining while the poop-poop was boring. I played at least as much just laughing at the poop-punk as I did to kill the poop-poop while waiting for it to become amusing.
Suggestions would include giving a few reactions to the poop-poop instead of just the 2 it has. Maybe let it grow with the right foods. Too much soda and it could become runny. Even turning green with too much broccoli?
To make it more challenging, it could poop out another poop to feed. Then there'd be 2 poops. And if it reaches the same point, each of those could poop another poop making 4 poops. You win if you fill the screen with poop?
But again, I never played this sort of game so that may go against what you had in mind.
I don't think the rest of my ideas are suitable for a family oriented forum...