+100 points for using Chopin's Funeral March for the game over theme. Sprite art is very cute and expressive as well. The game itself is decently fun and it's amazing you got it done in such a short amount of time. It gets overwhelming like any good arcade game of the time would be, but I have a couple suggestions for what I'd like to see added in the future (If you're not done with the project, which is fine too, you did a solid job and you should be proud of the work you've done already).
I think adding a Mario Bros style POW block could go a long way in getting the player to play the game more. When enough crabs reach the bottom it can start to feel kinda hopeless and defeating, having a couple screen clears (for the enemies on the ground at least) ready would help the game's longevity and add another strategic element. Another thing I'd add is some kind of item that can hit multiple crabs at once, whether it's like a koopa shell or Donkey Kong hammer. Just something to make way for a good score multiplier that'll make the player feel like they can really optimize their high score.
But those aren't really problems with the game, those are just suggestions from a worthless idea guy. Great job on your game. Punch those crabs!
Edit: You're amazing for including the source code with your game, big ups. I'll see if I can include it in my game as an extra minigame. I had an idea for the minigames to all run on a Windows XP spoof OS with some of the games running in a Nesticle like parody emulator, this'll fit right in.