Thanks for the feedback everybody, I really appreciate it! I see the bug that you guys are talking about with the game freezing when an enemy reaches the bridge; that was supposed to be another game over screen. Sorry about that! I'll update soon, but for now, if any more people see this before they play, if the game freezes, just refresh the page. It's a game over, so you'll have to start again anyway.
Edit: Updated! Game over works properly now.